M16 rifle
Overview
 
The M16 is the United States military designation for the AR-15
AR-15
The AR-15 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed semi-automatic rifle, with a rotating-lock bolt, actuated by direct impingement gas operation. It is manufactured with the extensive use of aluminum alloys and synthetic materials....

 rifle adapted for both semi-automatic and full-automatic fire. Colt
Colt's Manufacturing Company
Colt's Manufacturing Company is a United States firearms manufacturer, whose first predecessor corporation was founded in 1836 by Sam Colt. Colt is best known for the engineering, production, and marketing of firearms over the later half of the 19th and the 20th century...

 purchased the rights to the AR-15 from ArmaLite
ArmaLite
ArmaLite is the name of a small arms engineering facility founded in the early 1950s, and once associated with the Fairchild Engine and Airplane Corporation. ArmaLite was formally incorporated as a subdivision of Fairchild on October 1, 1954...

, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO cartridge. The rifle entered United States Army
United States Army
The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 service and was deployed for jungle warfare
Jungle warfare
Jungle warfare is a term used to cover the special techniques needed for military units to survive and fight in jungle terrain.It has been the topic of extensive study by military strategists, and was an important part of the planning for both sides in many conflicts, including World War II and the...

 operations in South Vietnam
South Vietnam
South Vietnam was a state which governed southern Vietnam until 1975. It received international recognition in 1950 as the "State of Vietnam" and later as the "Republic of Vietnam" . Its capital was Saigon...

 in 1963, becoming the U.S.
Encyclopedia
The M16 is the United States military designation for the AR-15
AR-15
The AR-15 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed semi-automatic rifle, with a rotating-lock bolt, actuated by direct impingement gas operation. It is manufactured with the extensive use of aluminum alloys and synthetic materials....

 rifle adapted for both semi-automatic and full-automatic fire. Colt
Colt's Manufacturing Company
Colt's Manufacturing Company is a United States firearms manufacturer, whose first predecessor corporation was founded in 1836 by Sam Colt. Colt is best known for the engineering, production, and marketing of firearms over the later half of the 19th and the 20th century...

 purchased the rights to the AR-15 from ArmaLite
ArmaLite
ArmaLite is the name of a small arms engineering facility founded in the early 1950s, and once associated with the Fairchild Engine and Airplane Corporation. ArmaLite was formally incorporated as a subdivision of Fairchild on October 1, 1954...

, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO cartridge. The rifle entered United States Army
United States Army
The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 service and was deployed for jungle warfare
Jungle warfare
Jungle warfare is a term used to cover the special techniques needed for military units to survive and fight in jungle terrain.It has been the topic of extensive study by military strategists, and was an important part of the planning for both sides in many conflicts, including World War II and the...

 operations in South Vietnam
South Vietnam
South Vietnam was a state which governed southern Vietnam until 1975. It received international recognition in 1950 as the "State of Vietnam" and later as the "Republic of Vietnam" . Its capital was Saigon...

 in 1963, becoming the U.S. military's standard service rifle
Service rifle
The service rifle of a given army or armed force is that which it issues as standard to its soldiers. In modern forces, this is typically a highly versatile and rugged assault rifle suitable for use in nearly all theatres and environments...

 of the Vietnam War
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

 by 1969, replacing the M14 rifle
M14 rifle
The M14 rifle, formally the United States Rifle, 7.62 mm, M14, is an American selective fire automatic rifle firing 7.62x51mm NATO  ammunition. It was the standard issue U.S. rifle from 1959 to 1970. The M14 was used for U.S...

 in that role. The U.S. Army retained the M14 in CONUS
Conus
Conus is a large genus of small to large predatory sea snails, marine gastropod molluscs, with the common names of cone snails, cone shells or cones. This genus is placed in the subfamily Coninae within the family Conidae. Geologically speaking, the genus is known from the Eocene to the Recent ...

, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, and South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...

 until 1970. Since the Vietnam War, the M16 rifle family has been the primary service rifle of the U.S. armed forces.

The M16 has also been widely adopted by other militaries around the world. Total worldwide production of M16-style weapons since the design's inception has been approximately 8 million, making it the most-produced firearm of its caliber. As of 2010, the M16 is being phased out in the United States Army, and is being replaced by the M4 carbine
M4 carbine
The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 designed by Eugene Stoner and made by ArmaLite. It is a shorter and lighter variant of the M16A2 assault rifle, with 80% parts commonality.It is a gas-operated,...

, which is itself a shortened derivative of the M16A2. The M16 could be supplemented by the Individual Carbine beginning in 2014 if procurement of a new weapon is attained, if funds allow. This program is for the US Army. While all other services will stay with current M-16s and M-4 series weapons.

Introduction

The M16 is a lightweight, 5.56 mm, air-cooled, gas-operated
Gas-operated reloading
Gas-operation is a system of operation used to provide energy to operate autoloading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed...

, magazine
Magazine (firearm)
A magazine is an ammunition storage and feeding device within or attached to a repeating firearm. Magazines may be integral to the firearm or removable . The magazine functions by moving the cartridges stored in the magazine into a position where they may be loaded into the chamber by the action...

-fed assault rifle
Assault rifle
An assault rifle is a selective fire rifle that uses an intermediate cartridge and a detachable magazine. Assault rifles are the standard infantry weapons in most modern armies...

, with a rotating bolt
Rotating bolt
Rotating bolt is a method of locking originally developed by Ferdinand Ritter von Mannlicher and found in his Steyr-Mannlicher M1895 straight-pull bolt-action rifle designed for and issued to the Austro-Hungarian Army...

, actuated by direct impingement
Direct impingement
Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly to the bolt carrier or slide assembly to cycle the action.- Evaluation :...

 gas operation. The rifle is made of steel, 7075 aluminum alloy, composite plastics and polymer materials.

In the early 1960s, the U.S. Air Force
United States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

's rifle, the M16, and the Army's XM16E1, were the first versions of the M16 rifle fielded. Soon the U.S. Army standardized an upgrade of the XM16E1 as the M16A1 rifle, an M16 with a forward assist
Forward assist
The forward assist on a rifle is a button found commonly on M16 and AR-15 styled rifles, usually located near the bolt closure, that when hit will push the bolt carrier forward, ensuring that the bolt is locked. In order to ensure that the extractor is clipped around the rim of the shell, the...

 feature and other improvements requested by the Army. All of the early versions were chambered to fire the M193/M196 cartridge in the semi
Semi-automatic firearm
A semi-automatic, or self-loading firearm is a weapon which performs all steps necessary to prepare the weapon to fire again after firing—assuming cartridges remain in the weapon's feed device or magazine...

-automatic and the automatic
Automatic firearm
An automatic firearm is a firearm that loads another round mechanically after the first round has been fired.The term can be used to refer to semi-automatic firearms, which fire one shot per single pull of the trigger , or fully automatic firearms, which will continue to load and fire ammunition...

 firing modes. This occurred in the early 1960s, with the Army issuing it in late 1964. Commercial AR-15s were first issued to Special Forces troops in spring of 1964.

The M16A2 rifle entered service in the 1980s, being ordered in large scale by 1987, chambered to fire the standard NATO cartridge, the Belgian-designed M855/M856 cartridge. The M16A2 is a select-fire rifle (semi-automatic fire, three-round-burst fire) incorporating design elements requested by the Marine Corps: an adjustable, windage rear-sight; a stock 5/8 in longer; heavier barrel; case deflector for left-hand shooters; and cylindrical handguards. The fire mode selector is on the receiver's left side.

The M16A3 rifle is an M16A2 rifle with an M16A1's fire control group (semi-automatic fire, automatic fire) that is used only by the U.S. Navy.

The M16A4 rifle was standard issue for the United States Marine Corps
United States Marine Corps
The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...

 in Operation Iraqi Freedom since 2004; it replaced the M16A2 in front line units. In the U.S. Army the M16A2 rifle is being supplemented with two rifle models, the M16A4 and the M4 carbine
M4 carbine
The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 designed by Eugene Stoner and made by ArmaLite. It is a shorter and lighter variant of the M16A2 assault rifle, with 80% parts commonality.It is a gas-operated,...

 as the standard issue assault rifle. The M16A4 has a flat-top receiver developed for the M4 carbine, a handguard with four Picatinny rail
Picatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...

s for mounting a sight, laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

, night vision device, forward handgrip, removable handle, or a flashlight.

The M16 rifle is principally manufactured by Colt and Fabrique Nationale de Herstal
Fabrique Nationale de Herstal
Fabrique Nationale d'Herstal — self identified as FN Herstal and often referred to as Fabrique Nationale or simply FN — is a firearms manufacturer located in Herstal, Belgium....

 (under a U.S. military contract since 1988 by FNH-USA; currently in production since 1991, primarily M16A2, A3, and A4), with variants made elsewhere in the world. Versions for the U.S. military have also been made by H & R Firearms
H & R Firearms
H & R 1871, LLC is a manufacturer of firearms under the Harrington & Richardson and New England Firearms trademarks...

 General Motors
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...

 Hydramatic
Hydramatic
Hydramatic was an automatic transmission developed by both General Motors' Cadillac and Oldsmobile divisions. Introduced in 1939 for the 1940 model year vehicles, the Hydramatic was the first fully automatic mass-produced transmission developed for passenger automobile use.-History:During the...

 Division and most recently by Sabre Defence
Sabre Defence
Sabre Defence Industries is an American manufacturer of firearms and firearm parts and accessories. It is contracted by the United States armed forces for parts and mounts for the M2 Browning machine gun and Minigun...

. Semi-automatic versions of the AR-15 are popular recreational shooting rifles, with versions manufactured by other small and large manufacturers in the U.S.

Summary

ArmaLite sold its rights to the AR-15 to Colt in 1959. The AR-15 was first adopted in 1962 by the United States Air Force
United States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

, ultimately receiving the designation M16. The U.S. Army began to field the XM16E1 en masse in 1965 with most of them going to the Republic of Vietnam, and the newly organized and experimental Airmobile Divisions, the 1st Air Cavalry Division in particular. The U.S. Marine Corps in South Vietnam also experimented with the M16 rifle in combat during this period. The XM16E1 was standardized as the M16A1 in 1967. This version remained the primary infantry rifle of U.S. forces in South Vietnam until the end of the war in 1975, and remained with all U.S. military ground forces after it had replaced the M14
M14 rifle
The M14 rifle, formally the United States Rifle, 7.62 mm, M14, is an American selective fire automatic rifle firing 7.62x51mm NATO  ammunition. It was the standard issue U.S. rifle from 1959 to 1970. The M14 was used for U.S...

 service rifle
Service rifle
The service rifle of a given army or armed force is that which it issues as standard to its soldiers. In modern forces, this is typically a highly versatile and rugged assault rifle suitable for use in nearly all theatres and environments...

 in 1970 in CONUS
Conus
Conus is a large genus of small to large predatory sea snails, marine gastropod molluscs, with the common names of cone snails, cone shells or cones. This genus is placed in the subfamily Coninae within the family Conidae. Geologically speaking, the genus is known from the Eocene to the Recent ...

, Europe (Germany), and South Korea; when it was supplemented by the M16A2. During the early 1980s a roughly standardized load for this ammunition was adopted throughout NATO (see: 5.56x45mm NATO
5.56x45mm NATO
5.56×45mm NATO is a rifle cartridge developed in the United States and originally chambered in the M16 rifle. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries. It is derived from, but not identical to, the .223 Remington cartridge...

).

The M16A3 is a fully automatic variant of the M16A2, issued within the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

. The M16A2 is currently being supplemented by the M16A4, which incorporates the flattop receiver unit developed for the M4 carbine, and Picatinny rail
Picatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...

 system. M16A2s are still in stock with the U.S. Army and Marine Corps, but are used primarily by reserve and National Guard units as well as by the U.S. Air Force.

The M16 rifle design, including variant or modified version of it such as the Armalite
ArmaLite
ArmaLite is the name of a small arms engineering facility founded in the early 1950s, and once associated with the Fairchild Engine and Airplane Corporation. ArmaLite was formally incorporated as a subdivision of Fairchild on October 1, 1954...

/Colt AR-15
AR-15
The AR-15 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed semi-automatic rifle, with a rotating-lock bolt, actuated by direct impingement gas operation. It is manufactured with the extensive use of aluminum alloys and synthetic materials....

 series, AAI M15 rifle; AP74; EAC J-15; SGW XM15A; any 22-caliber rimfire variant, including the Mitchell M16A-1/22, Mitchell M16/22, Mitchell CAR-15/22, and AP74 Auto Rifle, is a prohibited and restricted weapon in Canada.

Project SALVO

In 1948, the Army organized the civilian Operations Research Office
Operations Research Office
The Operations Research Office was a civilian military research center founded in 1948 by the United States Army. It was run under contract by Johns Hopkins University. The organization's offices were originally at Fort McNair, Washington, D.C. They moved to Chevy Chase, Maryland in 1952...

, mirroring similar operations research
Operations research
Operations research is an interdisciplinary mathematical science that focuses on the effective use of technology by organizations...

 organizations in the United Kingdom. One of their first efforts, Project ALCLAD, studied body armor and the conclusion was that they would need to know more about battlefield injuries in order to make reasonable suggestions. Over 3 million battlefield reports from World War I and World War II were analyzed and over the next few years they released a series of reports on their findings.

The conclusion was that most combat takes place at short range. In a highly mobile war, combat teams ran into each other largely by surprise; and the team with the higher firepower tended to win. They also found that the chance of being hit in combat was essentially random; accurate "aiming" made little difference because the targets no longer sat still. The number one predictor of casualties was the total number of bullets fired. Other studies of behavior in battle revealed that many U.S. infantrymen (as many as 2/3) never actually fired their rifles in combat. By contrast, soldiers armed with rapid fire weapons were much more likely to have fired their weapons in battle. These conclusions suggested that infantry should be equipped with a fully automatic rifle of some sort in order to increase the actual firepower of regular soldiers. It was also clear, however, that such weapons dramatically increased ammunition use and in order for a rifleman to be able to carry enough ammunition for a firefight he would have to carry something much lighter.

Existing rifles met none of these criteria. Although it appeared the new 7.62 mm T44 (precursor to the M14
M14 rifle
The M14 rifle, formally the United States Rifle, 7.62 mm, M14, is an American selective fire automatic rifle firing 7.62x51mm NATO  ammunition. It was the standard issue U.S. rifle from 1959 to 1970. The M14 was used for U.S...

) would increase the rate of fire, its heavy 7.62 mm NATO cartridge made carrying significant quantities of ammunition difficult. Moreover, the length and weight of the weapon made it unsuitable for short range combat situations often found in jungle and urban combat or mechanized warfare, where a smaller and lighter weapon could be brought to bear faster.

These efforts were noticed by Colonel René Studler, U.S. Army Ordnance's Chief of Small Arms Research and Development. Col. Studler asked the Aberdeen Proving Ground
Aberdeen Proving Ground
Aberdeen Proving Ground is a United States Army facility located near Aberdeen, Maryland, . Part of the facility is a census-designated place , which had a population of 3,116 at the 2000 census.- History :...

 to submit a report on the smaller caliber weapons. A team led by Donald Hall, director of program development at Aberdeen, reported that a .22 inch (5.56 mm) round fired at a higher velocity would have performance equal to larger rounds in most combat. With the higher rate of fire possible due to lower recoil it was likely such a weapon would inflict more casualties on the enemy. His team members, notably William C. Davis, Jr. and Gerald A. Gustafson, started development of a series of experimental .22 (5.56 mm) cartridges. In 1955, their request for further funding was denied.

A new study, Project SALVO, was set up to try to find a weapon design suited to real-world combat. Running between 1953 and 1957 in two phases, SALVO eventually suggested that a weapon firing four rounds into a 20 inches (508 mm) area would double the hit probability of existing semi-automatic weapons.

In the second phase, SALVO II, several experimental weapons concepts were tested. Irwin Barr of AAI Corporation
AAI Corporation
AAI Corporation is an aerospace and defense development and manufacturing firm in Hunt Valley, Maryland, USA. It is formerly a wholly owned subsidiary of United Industrial Corporation, AAI was acquired by Textron in 2007 and currently is an operating unit of Textron Systems Corporation...

 introduced a series of flechette
Flechette
A flechette is a pointed steel projectile, with a vaned tail for stable flight. The name comes from French , "little arrow" or "dart", and sometimes retains the acute accent in English: fléchette.-Bulk and artillery use:...

 weapons, starting with a shotgun shell containing 32 darts and ending with single-round flechette "rifles". Winchester
Winchester Repeating Arms Company
The Winchester Repeating Arms Company was a prominent American maker of repeating firearms, located in New Haven, Connecticut. The Winchester brand is today used under license by two subsidiaries of the Herstal Group, Fabrique Nationale of Belgium and the Browning Arms Company of Morgan, Utah.-...

 and Springfield Armory
Springfield Armory
The Springfield Armory, located in the City of Springfield, Massachusetts - from 1777 until its closing in 1968 - was the primary center for the manufacture of U.S. military firearms. After its controversial closing during the Vietnam War, the Springfield Armory was declared Western Massachusetts'...

 offered multiple barrel
Multiple Barrel Firearm
A Multiple barrel firearm is a firearm of any type with more than one barrel, usually to increase the rate of fire/hitting probability and to reduce barrel erosion/overheating.-Definition:...

 weapons, while ORO's own design used two .22, .25 or .27 caliber bullets loaded into a single .308 Winchester
.308 Winchester
The .308 Winchester is a rifle cartridge and is the commercial cartridge upon which the military 7.62x51mm NATO centerfire cartridge is based. The .308 Winchester was introduced in 1952, two years prior to the NATO adoption of the 7.62x51mm NATO T65...

 or .30-06
.30-06 Springfield
The .30-06 Springfield cartridge or 7.62×63mm in metric notation, was introduced to the United States Army in 1906 and standardized, and was in use until the 1960s and early 1970s. It replaced the .30-03, 6 mm Lee Navy, and .30 US Army...

 cartridge.

Eugene Stoner

Meanwhile testing of the 7.62 mm T44 continued, and Fabrique Nationale
Fabrique Nationale de Herstal
Fabrique Nationale d'Herstal — self identified as FN Herstal and often referred to as Fabrique Nationale or simply FN — is a firearms manufacturer located in Herstal, Belgium....

 also submitted their new FN FAL
FN FAL
The Fusil Automatique Léger or FAL is a self-loading, selective fire battle rifle produced by the Belgian armaments manufacturer Fabrique Nationale de Herstal . During the Cold War it was adopted by many North Atlantic Treaty Organization countries, with the notable exception of the United States...

 via the American firm Harrington & Richardson as the T48. The T44 was selected as the new battle rifle for the U.S. Army (rechristened the M14) despite a strong showing by the T48.

In 1954, Eugene Stoner
Eugene Stoner
Eugene Morrison Stoner is the man most associated with the design of the AR-15, which was adopted by the US military as the M16...

 of the newly formed ArmaLite
ArmaLite
ArmaLite is the name of a small arms engineering facility founded in the early 1950s, and once associated with the Fairchild Engine and Airplane Corporation. ArmaLite was formally incorporated as a subdivision of Fairchild on October 1, 1954...

 helped develop the 7.62 mm AR-10
AR-10
The AR-10 is an American 7.62 mm battle rifle developed by Eugene Stoner in the late 1950s at ArmaLite, then a division of the Fairchild Aircraft Corporation...

. Springfield's T44 and similar entries were conventional rifles using wood for the "furniture" and otherwise built entirely of steel using mostly forged and machined parts. ArmaLite was founded specifically to bring the latest in designs and alloys to firearms design, and Stoner felt he could easily beat the other offerings.

The AR-10's receiver was made of forged
Forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons...

 and milled
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...

 aluminium alloy instead of steel. The barrel was mated to the receiver by a separate hardened steel extension to which the bolt locked. This allowed a lightweight aluminum receiver to be used while still maintaining a steel-on-steel lockup. The bolt was operated by high-pressure combustion gases taken from a hole in the middle of the barrel directly through a tube above the barrel to a cylinder created in the bolt carrier with the bolt carrier itself acting as a piston. Traditional rifles located this cylinder and piston close to the gas vent. The stock
Stock (firearm)
A stock, also known as a buttstock or shoulder stock, is a part of a rifle or other firearm, to which the barrel and firing mechanism are attached, that is held against one's shoulder when firing the gun. Stocks are also found on crossbows though a crossbow stock is more properly referred to as a...

 and grips were made of a glass-reinforced plastic
Glass-reinforced plastic
Fiberglass , is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass. It is also known as GFK ....

 shell over a rigid foam plastic core. The muzzle brake
Muzzle brake
Muzzle brakes and recoil compensators are devices that are fitted to the muzzle of a firearm or cannon to redirect propellant gases with the effect of countering both recoil of the gun and unwanted rising of the barrel during rapid fire...

 was fabricated from titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

. Over Stoner's objections, various experimental composite and 'Sullaloy' aluminum barrels were fitted to some AR-10 prototypes by ArmaLite's president, George Sullivan. The Sullaloy barrel was made entirely of heat-treated aluminum, while the composite barrels used aluminum extruded over a thin stainless steel liner.

Meanwhile the layout of the weapon itself was also somewhat different. Previous designs generally placed the sights directly on the barrel, using a bend in the stock to align the sights at eye level while transferring the recoil down to the shoulder. This meant that the weapon tended to rise when fired making it very difficult to control during fully automatic fire. The ArmaLite team used a solution previously used on weapons such as the German
Nazi Germany
Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...

 FG 42
FG 42
The FG 42 was a selective fire battle rifle produced in Nazi Germany during World War II...

 and Johnson light machine gun; they located the barrel in line with the stock, well below eye level, and raised the sights to eye level. The rear sight was built into a carrying handle over the receiver.

Despite being over 2 lb (0.90718474 kg) lighter than the competition, the AR-10 offered significantly greater accuracy and recoil control. Two prototype rifles were delivered to the U.S. Army's Springfield Armory for testing late in 1956. At this time, the U.S. armed forces were already two years into a service rifle evaluation program, and the AR-10 was a newcomer with respect to older, more fully developed designs. Over Stoner's continued objections, George Sullivan had insisted that both prototypes be fitted with composite aluminum/steel barrels. Shortly after a composite barrel burst on one prototype in 1957, the AR-10 was rejected. The AR-10 was later produced by a Dutch firm, Artillerie Inrichtingen, and saw limited but successful military service with several foreign nations such as Sudan, Guatemala, and Portugal. Portugal deployed a number of AR-10s for use by its airborne (Caçadores Pára-quedista) battalions, and the rifle saw considerable combat service in Portugal's counter-insurgency campaigns in Angola and Mozambique. Some AR-10 rifles were still in service with airborne forces serving during the withdrawal from Portuguese Timor in 1975.

CONARC

In 1957, a copy of Gustafson's funding request from 1955 found its way into the hands of General Willard G. Wyman
Willard G. Wyman
Willard Gordon Wyman was a United States Army four star general who served as Commanding General, U.S. Continental Army Command from 1956 to 1958....

, commander of the U.S. Continental Army Command. He immediately put together a team to develop a .223 caliber (5.56 mm) weapon for testing. Their finalized request called for a select-fire weapon of 6 pounds (2.7 kg) when loaded with 20 rounds of ammunition. The bullet had to penetrate a standard U.S. steel helmet
M1 Helmet
The M1 helmet is a combat helmet that was used by the American military from World War II until it was succeeded by the PASGT helmet beginning in 1985. For over forty years, the M1 was standard issue for the U.S...

, body armor, or a steel plate of 0.135 inches (3.4 mm) and retain a velocity in excess of the speed of sound at 500 yards (457.2 m), while equaling or exceeding the "wounding" ability of the .30 Carbine
.30 Carbine
The .30 Carbine is the cartridge used in the M1 Carbine introduced in the 1940s. It is an intermediate round designed to be fired from the M1 carbine's 18-inch barrel.-History:...

.

Wyman had seen the AR-10 in an earlier demonstration, and impressed by its performance he personally suggested that ArmaLite enter a weapon for testing using a 5.56 mm cartridge designed by Winchester. Their first design, using conventional layout and wooden furniture, proved to be too light. When combined with a conventional stock, recoil was excessive in fully automatic fire. Their second design was simply a scaled-down AR-10, and immediately proved much more controllable. Winchester entered the LMR
Winchester LMR
The Winchester LMR is a prototype rifle that was developed for military use but was sidelined in 1964 by the AR-15....

, a design based loosely on their M1 carbine
M1 Carbine
The M1 carbine is a lightweight, easy to use semi-automatic carbine that became a standard firearm for the U.S. military during World War II, the Korean War and the Vietnam War, and was produced in several variants. It was widely used by U.S...

, and Earle Harvey of Springfield attempted to enter a design, but was overruled by his superiors at Springfield, who refused to divert resources from the T44. In the end, ArmaLite's AR-15
AR-15
The AR-15 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed semi-automatic rifle, with a rotating-lock bolt, actuated by direct impingement gas operation. It is manufactured with the extensive use of aluminum alloys and synthetic materials....

 had no competition. The lighter round allowed the rifle to be scaled down, and was smaller and lighter than the previous AR-10. The AR-15 weighed only around 5.5 pounds (2.5 kg) empty, and 6 pounds (2.7 kg) loaded (with a 20 round magazine).

During testing in March 1958, rainwater caused the barrels of both the ArmaLite and Winchester rifles to burst, causing the Army to once again press for a larger round, this time at 0.258 in (6.6 mm). Nevertheless, they suggested continued testing for cold-weather suitability in Alaska. Stoner was later asked to fly in to replace several parts, and when he arrived he found the rifles had been improperly reassembled. When he returned he was surprised to learn that they too had rejected the design even before he had arrived; their report also endorsed the 0.258 in (6.6 mm) round. After reading these reports, General Maxwell Taylor became dead-set against the design, and pressed for continued production of the M14.

Not all the reports were negative. In a series of mock-combat situations testing the AR-15, M14
M14 rifle
The M14 rifle, formally the United States Rifle, 7.62 mm, M14, is an American selective fire automatic rifle firing 7.62x51mm NATO  ammunition. It was the standard issue U.S. rifle from 1959 to 1970. The M14 was used for U.S...

 and AK-47
AK-47
The AK-47 is a selective-fire, gas-operated 7.62×39mm assault rifle, first developed in the Soviet Union by Mikhail Kalashnikov. It is officially known as Avtomat Kalashnikova . It is also known as a Kalashnikov, an "AK", or in Russian slang, Kalash.Design work on the AK-47 began in the last year...

, the Army found that the AR-15's small size and light weight allowed it to be brought to bear much more quickly, just as CONARC had suggested. Their final conclusion was that an 8-man team equipped with the AR-15 would have the same firepower as a current 11-man team armed with the M14. U.S. troops were able to carry more than twice as much 5.56×45mm ammunition as 7.62x51mm for the same weight, which would allow them a better advantage against a typical NVA
Vietnam People's Army
The Vietnam People's Army is the armed forces of Vietnam. The VPA includes: the Vietnamese People's Ground Forces , the Vietnam People's Navy , the Vietnam People's Air Force, and the Vietnam Marine Police.During the French Indochina War , the VPA was often referred to as the Việt...

 unit armed with AK-47s.

At this point, Fairchild had spent $1.45 million in development expenses, and wished to divest itself of its small-arms business. Fairchild sold production rights for the AR-15 to Colt Firearms in December 1959, for only $75,000 cash and a 4.5% royalty on subsequent sales. In 1960, ArmaLite was reorganized, and Stoner left the company.

M16 adoption

Curtis LeMay
Curtis LeMay
Curtis Emerson LeMay was a general in the United States Air Force and the vice presidential running mate of American Independent Party candidate George Wallace in 1968....

 viewed a demonstration of the AR-15 in July 1960. In the summer of 1961, General LeMay had been promoted to the position of USAF Chief of Staff, and requested an order of 80,000 AR-15s for the U.S. Air Force. However under the recommendation of General Maxwell D. Taylor
Maxwell D. Taylor
General Maxwell Davenport "Max" Taylor was an United States Army four star general and diplomat of the mid-20th century, who served as the fifth Chairman of the Joint Chiefs of Staff after having been appointed by the President of the United States John F...

, who advised the Commander in Chief that having two different calibers within the military system at the same time would be problematic, President Kennedy
John F. Kennedy
John Fitzgerald "Jack" Kennedy , often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963....

 turned down the request. However, Advanced Research Projects Agency, which had been created in 1958 in response to the Soviet Sputnik program, embarked on project AGILE
Project AGILE
Project AGILE was an ARPA project in the 1960s that investigated means for engaging in remote, limited warfare of an asymmetric type. The research was intended for use in providing US support to countries engaged in fighting Communist insurgents, particularly in Vietnam and...

 in the spring of 1961. AGILE's priority mission was to devise inventive fixes to the communist problem in South Vietnam. In October 1961, William Godel, a senior man at ARPA, sent 10 AR-15s to South Vietnam to let the allies test them. The reception was enthusiastic, and in 1962 another 1,000 AR-15s were sent to South Vietnam. Special Operations
Special operations
Special operations are military operations that are considered "special" .Special operations are typically performed independently or in conjunction with conventional military operations. The primary goal is to achieve a political or military objective where a conventional force requirement does...

 units and advisers working with the South Vietnamese troops filed battlefield reports lavishly praising the AR-15 and the stopping effectiveness of the 5.56 mm cartridge, and pressed for its adoption. However, what no one knew, except the men directly using the AR-15s in Vietnam, were the devastating kills made by the new rifle, photographs of which, showing enemy casualties made by the .223 (5.56 mm) bullet remained classified into the 1980s.

The damage caused by the .223 (5.56mm) "varmint" bullet was observed and originally believed to be caused by "tumbling" due to the slow 1 in 14 inches (355.6 mm) rifling twist rate. However, this twist rate only made the bullet less stable in air. Any pointed lead core bullet will turn base over point ("tumble") after penetration in flesh, because the center of gravity is aft of the center of the projectile. The large wounds observed by soldiers in Vietnam were actually caused by projectile fragmentation, which was created by a combination of the projectile's velocity and construction.

U.S. Secretary of Defense Robert McNamara now had two conflicting views: the ARPA report favoring the AR-15 and the Pentagon's position on the M14. Even President John F. Kennedy
John F. Kennedy
John Fitzgerald "Jack" Kennedy , often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963....

 expressed concern, so McNamara ordered Secretary of the Army Cyrus Vance
Cyrus Vance
Cyrus Roberts Vance was an American lawyer and United States Secretary of State under President Jimmy Carter from 1977 to 1980...

 to test the M14, the AR-15 and the AK-47. The Army's test report stated only the M14 was suitable for Army use, but Vance wondered about the impartiality of those conducting the tests. He ordered the Army Inspector General to investigate the testing methods used, who reported that the testers showed favor to the M14.
Secretary Robert McNamara ordered a halt to M14 production in January 1963, after receiving reports that M14 production was insufficient to meet the needs of the armed forces. Secretary McNamara had long been a proponent of weapons program consolidation among the armed services. At the time, the AR-15 was the only rifle that could fulfill a requirement of a "universal" infantry weapon for issue to all services. McNamara ordered the weapon be adopted unmodified, in its current configuration, for immediate issue to all services, despite receiving reports noting several deficiencies with the M16 as a service rifle, including the lack of a chrome-lined
Chrome plating
Chrome plating, often referred to simply as chrome, is a technique of electroplating a thin layer of chromium onto a metal object. The chromed layer can be decorative, provide corrosion resistance, ease cleaning procedures, or increase surface hardness.-Process:A component to be chrome plated will...

 bore and chamber, the 5.56 mm projectile's instability under arctic conditions, and the fact that large quantities of 5.56 mm ammunition required for immediate service were not available. In addition, the Army insisted on the inclusion of a forward assist
Forward assist
The forward assist on a rifle is a button found commonly on M16 and AR-15 styled rifles, usually located near the bolt closure, that when hit will push the bolt carrier forward, ensuring that the bolt is locked. In order to ensure that the extractor is clipped around the rim of the shell, the...

 to help push the bolt into battery in the event that a cartridge failed to seat in the chamber through fouling or corrosion. Colt had argued the rifle was a self-cleaning design, requiring little or no maintenance. Colt, Eugene Stoner, and the U.S. Air Force believed that a forward assist needlessly complicated the rifle, adding about $4.50 to its procurement cost with no real benefit. As a result, the design was split into two variants: the Air Force's M16 without the forward assist, and for the other service branches, the XM16E1 with the forward assist
Forward assist
The forward assist on a rifle is a button found commonly on M16 and AR-15 styled rifles, usually located near the bolt closure, that when hit will push the bolt carrier forward, ensuring that the bolt is locked. In order to ensure that the extractor is clipped around the rim of the shell, the...

.

In November 1963, McNamara approved the Army's order of 85,000 XM16E1s for jungle warfare operations; and to appease General LeMay, the Air Force was granted an order for another 19,000 M16s. Meanwhile, the Army carried out another project, the Small Arms Weapons Systems, on general infantry firearm needs in the immediate future. They recommended the immediate adoption of the weapon. Later that year the Air Force officially accepted their first batch as the United States Rifle, Caliber 5.56 mm, M16.

The Army immediately began to issue the XM16E1 to infantry units but the rifle was initially delivered without adequate cleaning supplies or instructions. When the M16 reached Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

 with U.S. troops in March 1965, reports of stoppages in combat began to surface. Often the gun suffered from a stoppage known as “failure to extract,” which meant that a spent cartridge case remained lodged in the chamber after a bullet flew out the muzzle. Although the M14 featured a chrome-lined
Chrome plating
Chrome plating, often referred to simply as chrome, is a technique of electroplating a thin layer of chromium onto a metal object. The chromed layer can be decorative, provide corrosion resistance, ease cleaning procedures, or increase surface hardness.-Process:A component to be chrome plated will...

 barrel and chamber to resist corrosion in combat conditions, neither the bore nor the chamber of the M16/XM16E1 was chrome-lined. Several documented accounts of troops killed by enemy fire with inoperable rifles broken-down for cleaning eventually brought a Congressional investigation.
The root cause of the stoppages turned out to be a problem with the powder for the ammunition. In 1964 when the Army was informed that DuPont
DuPont
E. I. du Pont de Nemours and Company , commonly referred to as DuPont, is an American chemical company that was founded in July 1802 as a gunpowder mill by Eleuthère Irénée du Pont. DuPont was the world's third largest chemical company based on market capitalization and ninth based on revenue in 2009...

 could not mass-produce the nitrocellulose-based powder to the specifications demanded by the M16, the Olin Mathieson Company provided a high-performance ball propellant of nitrocellulose and nitroglycerin. While the Olin WC 846 powder was capable of firing an M16 5.56 mm round at the desired 3300 ft (1,005.8 m) per second, it had the unintended consequence of increasing the automatic rate of fire from 850 to 1000 rounds per minute. This would leave behind dirty residue, making the M16 more likely to have a stoppage. The problem was resolved by fitting the M16 with a buffer system, slowing the rate of fire back down to 650 to 850 rounds per minute and outfitting all newly produced M16s with an anti corrosive chrome-plated chamber.

On February 28, 1967, the XM16E1 was standardized as the M16A1. Major revisions to the design followed. The rifle was given a chrome-lined chamber (and later, the entire bore) to eliminate corrosion and stuck cartridges, and the rifle's recoil mechanism was re-designed to accommodate Army-issued 5.56 mm ammunition. Rifle cleaning tools and powder solvents/lubricants were issued. Intensive training programs in weapons cleaning were instituted, and a comic book
Comic book
A comic book or comicbook is a magazine made up of comics, narrative artwork in the form of separate panels that represent individual scenes, often accompanied by dialog as well as including...

 style manual was circulated among the troops to demonstrate proper maintenance. The reliability problems of the M16 diminished quickly, although the rifle's reputation continued to suffer.

According to a February 1968 Department of Defense
United States Department of Defense
The United States Department of Defense is the U.S...

 report the M16 rifle achieved widespread acceptance by U.S. troops in Vietnam. Only 38 of 2100 individuals queried wanted to replace the M16 with another weapon. Of those 38, 35 wanted the CAR-15
CAR-15
The Colt Automatic Rifle-15 Military Weapons System or CAR-15 was a family of AR-15 and M16 rifle–based firearms marketed by Colt in the late 1960s and early 1970s. Due to their compact size, the short-barreled Colt Commando and XM177 versions of this family continued to be issued to the U.S...

 (a shorter version of the M16) instead.

NATO standards

In March 1970, the U.S. stated that all NATO forces should eventually adopt the 5.56x45mm cartridge. This shift represented a change in the philosophy of the military's long-held position about caliber size. By the middle of the 1970s, other armies were also looking at M16-style weapons. A NATO standardization effort soon started, and tests of various rounds were carried out starting in 1977. The U.S. offered their original 5.56x45mm design, the M193, with no modifications, but there were concerns about its penetration in the face of the wider introduction of body armor. In the end the Belgian 5.56x45mm SS109 round was chosen (STANAG
STANAG
STANAG is the NATO abbreviation for Standardization Agreement, which sets up processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the alliance. Each NATO state ratifies a STANAG and implements it within their own...

 4172). Their round was based on the U.S. cartridge but included a new 62 grain bullet design with a small steel tip added to improve penetration. The U.S. Marine Corps was first to adopt the round with the M16A2, introduced in 1982. This was to become the standard U.S. military rifle. The NATO 5.56x45mm standard ammunition produced for U.S. forces is designated M855.

Shortly after NATO's acceptance of the 5.56x45mm NATO
5.56x45mm NATO
5.56×45mm NATO is a rifle cartridge developed in the United States and originally chambered in the M16 rifle. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries. It is derived from, but not identical to, the .223 Remington cartridge...

 rifle cartridge in October 1980. Draft Standardization Agreement 4179 (STANAG 4179) was proposed in order to allow the military services of member nations easily to share rifle ammunition
Ammunition
Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...

 and magazines
Magazine (firearm)
A magazine is an ammunition storage and feeding device within or attached to a repeating firearm. Magazines may be integral to the firearm or removable . The magazine functions by moving the cartridges stored in the magazine into a position where they may be loaded into the chamber by the action...

 during operations, at the individual soldier level, in the interest of easing logistical concerns. The magazine chosen to become the STANAG magazine
STANAG magazine
A STANAG magazine is a type of detachable firearm magazine proposed by NATO in October 1980. Shortly after NATO's acceptance of the 5.56x45mm NATO rifle cartridge, Draft Standardization Agreement 4179 was proposed in order to allow the military services of member nations easily to share rifle...

was originally designed for the U.S. M16 rifle. Many NATO member nations, but not all, subsequently developed or purchased rifles with the ability to accept this type of magazine. However the standard was never ratified and remains a 'Draft STANAG'

The NATO Accessory Rail
NATO Accessory Rail
The NATO Accessory Rail , defined by the new modernization agreement STANAG 4694, is a new standard for mounting auxiliary equipment such as telescopic sights, tactical lights, laser aiming modules, night vision devices, reflex sights, foregrips, bipods, and bayonets to small arms such as rifles...

 STANAG 4694, or Picatinny rail
Picatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...

 STANAG 2324, or a "Tactical Rail" is a bracket used on M16 type rifles in order to provide a standardized mounting platform. The rail comprises a series of ridges with a T-shaped cross-section interspersed with flat "spacing slots". Scopes are mounted either by sliding them on from one end or the other; by means of a "rail-grabber" which is clamped to the rail with bolts, thumbscrews or levers; or onto the slots between the raised sections. The rail was originally for scopes. However, once established, the use of the system was expanded to other accessories, such as tactical lights, laser aiming modules, night vision devices, reflex sights, foregrips, bipods, and bayonets.

All current M16 type rifles are capable of launching NATO STANAG type 22mm rifle grenade
Rifle grenade
A rifle grenade is a grenade that uses a rifle-based launcher to permit a longer effective range than would be possible if the grenade was thrown by hand...

s from their integral flash hiders without the use of an adapter. These 22 mm grenade types range from powerful anti-tank rounds to simple finned tubes with a fragmentation hand grenade attached to the end. They come in the "standard" type which are propelled by a blank cartridge inserted into the chamber of the rifle. They also come in the "bullet trap" and "shoot through" types, as their names imply use live ammunition. The U.S. military does not generally use rifle grenades, however they are used by other Nations.

Currently, the M16 is in use by 15 NATO countries and more than 80 countries world wide.

Grenade launcher

The M203 40 mm grenade launcher
M203 grenade launcher
The M203 is a single shot 40 mm grenade launcher designed to attach to a rifle. It uses the same rounds as the older M79 break-action grenade launcher, which utilize the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was...

 was originally designed to be mounted on the M16 and its variants. It uses the same rounds as the older M79 "shotgun"-type grenade launcher, which utilize High-Low Propulsion System to keep recoil forces low. The M203 is versatile and compatible with many rifle models. It is widely used by the U.S. Military and is routinely seen on the M4 Carbine. The launcher can also be mounted onto the Canadian made C7, and requires the bottom handguard on the rifle to be removed in order to mount the launcher.

Design

The M16's receivers are made of 7075 aluminum alloy, its barrel, bolt, and bolt carrier of steel, and its handguards, pistol grip, and buttstock of plastics. Early models were especially lightweight at 6.5 pounds (2.9 kg) without magazine and sling. This was significantly less than older 7.62 mm "battle rifles" of the 1950s and 1960s. It also compares with the 6.5 pounds (2.9 kg) AKM
AKM
The AKM is a 7.62mm assault rifle designed by Mikhail Kalashnikov. It is an upgraded version of the AK-47 rifle and was developed in the 1950s....

 without magazine. M16A2 and later variants (A3 & A4) weigh more (8.5 lb (3.9 kg) loaded) because of the adoption of a thicker barrel profile. The thicker barrel is more resistant to damage when handled roughly and is also slower to overheat during sustained fire. Unlike a traditional "bull" barrel that is thick its entire length, the M16A2's barrel is only thick forward of the handguards. The barrel profile under the handguards remained the same as the M16A1 for compatibility with the M203 grenade launcher
M203 grenade launcher
The M203 is a single shot 40 mm grenade launcher designed to attach to a rifle. It uses the same rounds as the older M79 break-action grenade launcher, which utilize the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was...

. The rifle is the same length as the M16A2.

The M16 rifle fires the 5.56x45mm cartridge and can produce massive wounding effects when the bullet impacts at high velocity and yaws in tissue leading to fragmentation and rapid transfer of energy. This produces wounds that were so devastating that the International Committee of the Red Cross (ICRC) and many countries (Austria, Argentina, Belgium, Bolivia, Bulgaria, Burundi, Cambodia, Cyprus, Germany, Ireland, Latvia, Lithuania, Luxembourg, Mauritius, Mexico, Romania, Samoa, Slovenia, Sweden, Switzerland, etc.) considered the M16 to be an inhumane weapon.

One distinctive ergonomic feature is a plastic or metal stock directly behind the action, which contains a recoil
Recoil
Recoil is the backward momentum of a gun when it is discharged. In technical terms, the recoil caused by the gun exactly balances the forward momentum of the projectile and exhaust gasses, according to Newton's third law...

 spring. This serves the dual function of operating spring and recoil buffer. The stock being in line with the bore reduces muzzle rise, especially during automatic fire. Because recoil does not significantly shift the point of aim, faster follow-up shots are possible and user fatigue is reduced.

Another distinctive ergonomic feature is a carrying handle on top of the receiver, with an integrated rear sight assembly and charging handle. This design is a by-product of the original design where the carry handle served to protect the charging handle and mount a scope. In practice, the handle is rarely used to carry the weapon and doing so is expressly prohibited in many military organizations, as it is considered unsafe. Holding the weapon by the pistol grip provides quicker response time and better "muzzle awareness," while a shoulder sling provides a more convenient option when response time is not a concern. The "accessory rail" is also considered unsafe to use after the weapon has been fired for prolonged periods as enough heat, to melt flesh, will transfer from the receiver to the handle. More importantly, with the sight plane 2.5 in (63.5 mm) over the bore, the M16 has an inherent parallax problem that can be confounding to shooters. At closer ranges (typically inside 15–20 meters), the shooter must aim high in order to place shots where desired.

Newer models have a "flattop" upper receiver with a Picatinny rail
Picatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...

, to which the user can attach either a conventional sighting system or numerous optical devices such as night vision
Night vision
Night vision is the ability to see in low light conditions. Whether by biological or technological means, night vision is made possible by a combination of two approaches: sufficient spectral range, and sufficient intensity range...

 scopes.

The M16 utilizes direct impingement
Direct impingement
Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly to the bolt carrier or slide assembly to cycle the action.- Evaluation :...

 gas operation; energy from high-pressure gas tapped from a non-adjustable port built into the front sight assembly actuates the moving parts in the weapon. Combustion gases travel via a gas tube above the barrel directly into a chamber in the bolt carrier behind the bolt itself, pushing the carrier away from the bolt. This reduces the number of moving parts by eliminating the need for a separate piston and cylinder and it provides better performance in rapid fire by keeping reciprocating masses on the same axis as the bore.

The primary criticism of direct impingement is that fouling and debris from expended gunpowder is blown directly into the breech. As the superheated combustion gas travels down the tube, it expands and cools. This cooling causes vaporized matter to condense as it cools depositing a much greater volume of solids into the operating components of the action. The increased fouling can cause malfunctions if the rifle is not cleaned as frequently as should be. The amount of sooting deposits tends to vary with powder specification, caliber, and gas port design.

In April 2010 TACOM Life Cycle Management Command issued permission for soldiers to camouflage M4/M16 weapons with paint if given command approval.

Pre-Production ArmaLite AR-15

The weapon that eventually became the M16 series only had a vague resemblance to its offspring. The rifle was basically a scaled down AR-10
AR-10
The AR-10 is an American 7.62 mm battle rifle developed by Eugene Stoner in the late 1950s at ArmaLite, then a division of the Fairchild Aircraft Corporation...

 with an ambidextrous
Ambidexterity
Ambidexterity is the state of being equally adept in the use of both left and right appendages . It is one of the most famous varieties of cross-dominance. People that are naturally ambidextrous are rare, with only one out of one hundred people being naturally ambidextrous...

 charging handle located within the carrying handle, a narrower front sight "A" frame, and no flash suppressor.

AR-15 (Colt Models 601 & 602)

Colt's first two models produced after the acquisition of the rifle from ArmaLite were the 601 and 602, and these rifles were in many ways clones of the original ArmaLite rifle (in fact, these rifles were often found stamped Colt ArmaLite AR-15, Property of the U.S. Government caliber .223, and no reference to being a M16). The 601 and 602 are easily identified by their flat lower receivers without raised surfaces around the magazine well and occasionally green or brown furniture. The 601 was adopted first of any of the rifles by the USAF, and was quickly supplemented with the XM16 (Colt Model 602) and later the M16 (Colt Model 604) as improvements were made. There was also a limited purchase of 602s, and a number of both of these rifles found their way to a number of Special Operations units then operating in South East Asia, most notably the U.S. Navy SEALs
United States Navy SEALs
The United States Navy's Sea, Air and Land Teams, commonly known as Navy SEALs, are the U.S. Navy's principal special operations force and a part of the Naval Special Warfare Command as well as the maritime component of the United States Special Operations Command.The acronym is derived from their...

. The only major difference between the 601 and 602 is the switch from the original 1:14-inch rifling twist to the more common 1:12-inch twist. These weapons were equipped with a triangular charging handle and a bolt hold open device that lacked a raised lower engagement surface. The bolt hold open device had a slanted and serrated surface that had to be engaged with a bare thumb, index finger, or thumb nail because of the lack of this surface.

The United States Air Force continued to use the AR-15 marked rifles in various configurations into the 1990s.

M16

Variant originally adopted by the U.S. Air Force. This was the first M16 adopted operationally. This variant had triangular handguards, butt stocks without a compartment for the storage of a cleaning kit, a three-pronged flash suppressor, and no forward assist
Forward assist
The forward assist on a rifle is a button found commonly on M16 and AR-15 styled rifles, usually located near the bolt closure, that when hit will push the bolt carrier forward, ensuring that the bolt is locked. In order to ensure that the extractor is clipped around the rim of the shell, the...

. Bolt carriers were originally chrome plated and slick-sided, lacking forward assist notches. Later, the chrome plated carriers were dropped in favor of Army issued notched and parkerized carriers though the interior portion of the bolt carrier is still chrome-lined. The Air Force continued to operate these weapons until around 2001, at which time the Air Force converted all of its M16s to the M16A2 configuration.

The M16 was also adopted by the British SAS
Special Air Service
Special Air Service or SAS is a corps of the British Army constituted on 31 May 1950. They are part of the United Kingdom Special Forces and have served as a model for the special forces of many other countries all over the world...

, who used it to effect during the Falklands War
Falklands War
The Falklands War , also called the Falklands Conflict or Falklands Crisis, was fought in 1982 between Argentina and the United Kingdom over the disputed Falkland Islands and South Georgia and the South Sandwich Islands...

.

XM16E1 and M16A1 (Colt Model 603)

The U.S. Army XM16E1 was essentially the same weapon as the M16 with the addition of a forward assist
Forward assist
The forward assist on a rifle is a button found commonly on M16 and AR-15 styled rifles, usually located near the bolt closure, that when hit will push the bolt carrier forward, ensuring that the bolt is locked. In order to ensure that the extractor is clipped around the rim of the shell, the...

 and corresponding notches in the bolt carrier. The M16A1 was the finalized production model in 1967. To address issues raised by the XM16E1's testing cycle, a closed, bird-cage flash suppressor replaced the XM16E1's three-pronged flash suppressor which caught on twigs and leaves. Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued while barrels with chrome-plated chambers and later fully lined bores were introduced.

With these and other changes, the malfunction rate slowly declined and new soldiers were generally unfamiliar with early problems. A rib was built into the side of the receiver on the XM16E1 to help prevent accidentally pressing the magazine release button while closing the ejection port cover. This rib was later extended on production M16A1s to help in preventing the magazine release from inadvertently being pressed. The hole in the bolt that accepts the cam pin was crimped inward on one side, in such a way that the cam pin may not be inserted with the bolt installed backwards, which would cause failures to eject until corrected. The M16A1 remains in service in limited numbers in the United States but is still standard issue in many world armies.

M16A2

The development of the M16A2 rifle was originally requested by the United States Marine Corps
United States Marine Corps
The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...

 as a result of the USMC's combat experience in Vietnam with the XM16E1 and M16A1. The Marines were the first branch of the U.S. Armed Forces to adopt the M16A2 in the early/mid 1980s with the United States Army
United States Army
The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 following suit in the late 1980s. This rifle is now the current issue to Marine Corps' recruits in both MCRD San Diego and MCRD Parris Island. Modifications to the M16A2 were extensive. In addition to the new rifling, the barrel was made with a greater thickness in front of the front sight post to resist bending in the field and to allow a longer period of sustained fire without overheating. The rest of the barrel was maintained at the original thickness to enable the M203 grenade launcher
M203 grenade launcher
The M203 is a single shot 40 mm grenade launcher designed to attach to a rifle. It uses the same rounds as the older M79 break-action grenade launcher, which utilize the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was...

 to be attached. The front sight was now a square post with 4 detent positions, adjustable for vertical zeroing by using a cartridge, nail or special tool. A new adjustable rear sight was added, allowing the rear sight to be dialed in for specific range settings between 300 and 800 meters to take full advantage of the ballistic characteristics of the new SS109 rounds and to allow windage adjustments without the need of a tool or cartridge. The flash suppressor was again modified, this time to be closed on the bottom so it would not kick up dirt or snow when being fired from the prone position, and acting as a recoil compensator
Muzzle brake
Muzzle brakes and recoil compensators are devices that are fitted to the muzzle of a firearm or cannon to redirect propellant gases with the effect of countering both recoil of the gun and unwanted rising of the barrel during rapid fire...

. The front grip was modified from the original triangular shape to a round one, which better fitted smaller hands and could be fitted to older models of the M16. The new handguards were also symmetrical so that armories need not separate left and right spares. The handguard retention ring was tapered to make it easier to install and uninstall the handguards. A notch for the middle finger was added to the pistol grip, as well as more texture to enhance the grip. The buttstock was lengthened by 5/8 in. The new buttstock became ten times stronger than the original due to advances in polymer technology since the early 1960s. Original M16 stocks were made from fiberglass-impregnated resin; the newer stocks were engineered from DuPont Zytel glass-filled thermoset polymers. The new stock included a fully textured polymer buttplate for better grip on the shoulder, and retained a panel for accessing a small compartment inside the stock, often used for storing a basic cleaning kit. The heavier bullet reduces muzzle velocity
Muzzle velocity
Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...

 from 3200 feet per second (975.4 m/s), to about 3050 feet per second (929.6 m/s). The A2 also uses a faster twist rifling to allow the use of a trajectory-matched tracer round. A spent case deflector was incorporated into the upper receiver immediately behind the ejection port to prevent cases from striking left-handed users.

The action was also modified, replacing the fully automatic setting with a three-round burst setting. When using a fully automatic weapon, poorly trained troops often hold down the trigger and "spray" when under fire. The U.S. Army concluded that three-shot groups provide an optimum combination of ammunition conservation, accuracy and firepower.

M16A3

The M16A3 was a fully automatic variant of the M16A2 adopted in small numbers around the time of the introduction of the M16A2, primarily by the U.S. Navy for use by SEAL
United States Navy SEALs
The United States Navy's Sea, Air and Land Teams, commonly known as Navy SEALs, are the U.S. Navy's principal special operations force and a part of the Naval Special Warfare Command as well as the maritime component of the United States Special Operations Command.The acronym is derived from their...

, Seabee
Seabee
Seabees are members of the United States Navy construction battalions. The word Seabee is a proper noun that comes from the initials of Construction Battalion, of the United States Navy...

, and Security units. It features the M16A1 trigger group providing "safe", "semi-automatic", and "fully automatic" modes.

M16A4

The M16A4, now standard issue for front-line U.S. Marine Corps and some U.S. Army units, replaces the combination fixed carry handle/rear iron sight with a MIL-STD-1913 Picatinny rail
Picatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...

, allowing for the rifle to be equipped with a carry handle and/or most military and consumer scopes or sighting systems. Military issue rifles are also equipped with a Knight's Armament Company
Knight's Armament Company
Knight's Armament Company is an American firearms and firearms parts manufacturer.It is owned by C. Reed Knight and based in Titusville, Florida. KAC is best known for producing the Rail Interface System and the Rail Adapter System grips for military firearms...

 M5 RAS handguard, allowing vertical grips, lasers, tactical lights, and other accessories to be attached, coining the designation M16A4 MWS (or Modular Weapon System) in U.S. Army field manuals.

Colt Model 655 and 656 "Sniper" variants

With the expanding Vietnam War
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

, Colt developed two rifles of the M16 pattern for evaluation as possible light sniper or designated marksman rifles. The Colt Model 655 M16A1 Special High Profile was essentially a standard A1 rifle with a heavier barrel and a scope mount that attached to the rifle's carry handle. The Colt Model 656 M16A1 Special Low Profile had a special upper receiver with no carrying handle. Instead, it had a low-profile iron sight adjustable for windage and a Weaver base for mounting a scope, a precursor to the Colt and Picatinny rails. It also had a hooded front iron sight in addition to the heavy barrel. Both rifles came standard with either a Leatherwood/Realist scope 3–9× Adjustable Ranging Telescope. Some of them were fitted with a Sionics noise and flash suppressor. Neither of these rifles were ever standardized.

These weapons can be seen in many ways to be predecessors of the U.S. Army's SDM-R
United States Army Squad Designated Marksman Rifle
The United States Army Squad Designated Marksman Rifle is a heavily modified M16-series semi-automatic rifle intended to provide increased accuracy over range, giving infantry squads greater firepower.-Background:...

 and the USMC's SAM-R
U.S. Marine Corps Squad Advanced Marksman Rifle
The Squad Advanced Marksman Rifle is a semi-automatic rifle developed by and in service with the United States Marine Corps. It gives Marines the capability to provide precision fire in support of the rifle squad, providing precision fire in support of an assault, and aid in observation and...

 weapons.

XM177

In Vietnam, some soldiers were issued a carbine
Carbine
A carbine , from French carabine, is a longarm similar to but shorter than a rifle or musket. Many carbines are shortened versions of full rifles, firing the same ammunition at a lower velocity due to a shorter barrel length....

 version of the M16 called the XM177
CAR-15
The Colt Automatic Rifle-15 Military Weapons System or CAR-15 was a family of AR-15 and M16 rifle–based firearms marketed by Colt in the late 1960s and early 1970s. Due to their compact size, the short-barreled Colt Commando and XM177 versions of this family continued to be issued to the U.S...

. The XM177 had a shorter 10 in (254 mm) barrel and a telescoping stock, which made it substantially more compact. It also possessed a combination flash hider/sound moderator to reduce problems with muzzle flash and loud report. The USAF's GAU-5/A (XM177) and the U.S. Army's XM177E1 variants differed over the latter’s inclusion of a forward assist, although some GAU-5s do have the forward assist. The final USAF GAU-5A/A and U.S. Army XM177E2 had an 11.5 in (292 mm) barrel with a longer flash/sound suppressor. The lengthening of the barrel was to support the attachment of Colt's own XM148 40 mm grenade launcher. These versions were also known as the Colt Commando model commonly referenced and marketed as the CAR-15. The variants were issued in limited numbers to special forces, helicopter crews, Air Force pilots, Air Force Security Police Military Working Dog (MWD) handlers, officers, radio operators, artillerymen, and troops other than front line riflemen. Some USAF GAU-5A/As were later equipped with even longer 14.5 inches (368.3 mm) 1/12 rifled barrels as the two shorter versions were worn out. The 14.5 inches (368.3 mm) barrel allowed the use of MILES gear and for bayonets to be used with the sub-machine guns (as the USAF described them). By 1989 the USAF started to replace the earlier barrels with 1/7 rifled models.

Also used by the British SAS
Special Air Service
Special Air Service or SAS is a corps of the British Army constituted on 31 May 1950. They are part of the United Kingdom Special Forces and have served as a model for the special forces of many other countries all over the world...

, who used it to effect during the Falklands War
Falklands War
The Falklands War , also called the Falklands Conflict or Falklands Crisis, was fought in 1982 between Argentina and the United Kingdom over the disputed Falkland Islands and South Georgia and the South Sandwich Islands...

.

Colt Model 733

Colt also returned to the original "Commando
CAR-15
The Colt Automatic Rifle-15 Military Weapons System or CAR-15 was a family of AR-15 and M16 rifle–based firearms marketed by Colt in the late 1960s and early 1970s. Due to their compact size, the short-barreled Colt Commando and XM177 versions of this family continued to be issued to the U.S...

" idea, with its Model 733, essentially a modernized XM177E2 with many of the features introduced on the M16A2.

M231 Firing Port Weapon (FPW)

M231 Firing Port Weapon (FPW) is an adapted version of the M16 assault rifle for firing from ports on the M2 Bradley
M2 Bradley
The Bradley Fighting Vehicle is an American fighting vehicle platform manufactured by BAE Systems Land and Armaments, formerly United Defense.As with other infantry fighting vehicles, the Bradley is designed to transport infantry with armor protection while providing covering fire to suppress enemy...

. The infantry's normal M16s are too long for use in a "buttoned up" APC, so the FPW was developed to provide a suitable weapon for this role. Designed by the Rock Island Arsenal, the M231 FPW remains in service, although all but the rear two firing ports on the Bradley have been removed. The M231 FPW is often used by dismounted Mechanized Infantry
Mechanized infantry
Mechanized infantry are infantry equipped with armored personnel carriers , or infantry fighting vehicles for transport and combat ....

 during trench clearing and MOUT operations due to its compact size and high rate of fire. The M231 FPW fires from the open bolt and is only configured for fully automatic fire. The open bolt configuration gives the M231 a much higher cyclic rate of fire than the closed bolt operation of the M16A1.

Mk 4 Mod 0

The Mk 4 Mod 0 was a variant of the M16A1 produced for the U.S. Navy SEALs during the Vietnam War and adopted in April 1970. It differed from the basic M16A1 primarily in being optimized for maritime operations and coming equipped with a sound suppressor. Most of the operating parts of the rifle were coated in Kal-Guard, a hole of 0.25 inches (6.4 mm) was drilled through the stock and buffer tube for drainage, and an O-ring was added to the end of the buffer assembly. The weapon could reportedly be carried to the depth of 200 feet (60 m) without damage. The initial Mk 2 Mod 0 Blast Suppressor was based on the U.S. Army's Human Engineering Lab's (HEL) M4 noise suppressor. The HEL M4 vented gas directly from the action, requiring a modified bolt carrier. A gas deflector was added to the charging handle to prevent gas from contacting the user. Thus, the HEL M4 suppressor was permanently mounted though it allowed normal semi-automatic and automatic operation. If the HEL M4 suppressor were removed, the weapon would have to be manually loaded after each single shot. On the other hand, the Mk 2 Mod 0 blast suppressor was considered an integral part of the Mk 4 Mod 0 rifle, but it would function normally if the suppressor were removed. The Mk 2 Mod 0 blast suppressor also drained water much more quickly and did not require any modification to the bolt carrier or to the charging handle. In the late 1970s, the Mk 2 Mod 0 blast suppressor was replaced by the Mk 2 blast suppressor made by Knight's Armament Company (KAC). The KAC suppressor can be fully submerged and water will drain out in less than eight seconds. It will operate without degradation even if the M16A1 is fired at the maximum rate of fire. The U.S. Army replaced the HEL M4 with the much simpler Studies in Operational Negation of Insurgency and Counter-Subversion (SIONICS) MAW-A1 noise and flash suppressor.

Mark 12

Developed to increase the effective range of soldiers in the designated marksman role, the US Navy developed the Mark 12 Special Purpose Rifle (SPR). Configurations in service vary, but the core of the Mark 12 SPR is an 18" heavy barrel with muzzle brake and free float tube. This tube relieves pressure on the barrel caused by standard handguards and greatly increases the potential accuracy of the system. Also common are higher magnification optics ranging from the 6× power Trijicon ACOG to the Leupold Mark 4 Tactical rifle scopes. Firing Mark 262 Mod 0 ammunition with a 77gr Open tip Match bullet, the system has an official effective range of 600+ meters. However published reports of confirmed kills beyond 800 m from Iraq and Afghanistan are not uncommon.

M4 carbine

The M4 carbine was developed from various outgrowths of these designs, including a number of 14.5 inches (368 mm)-barreled A1 style carbines. The XM4 (Colt Model 727) started its trials in the mid-80s, with a barrel of 14.5 inches (368.3 mm). Officially adopted as a replacement for the M3 "Grease Gun"
M3 submachine gun
The M3 was an American .45-caliber submachine gun adopted for U.S. Army service on 12 December 1942, as the United States Submachine Gun, Cal. .45, M3. The M3 was designed as a more cost-effective alternative to the Thompson, optimized for mass production...

 (and the Beretta M9
M9 Pistol
The Beretta M9, formally Pistol, Semiautomatic, 9mm, M9, is a 9×19mm Parabellum pistol of the United States military adopted in 1985. It is essentially a military specification Beretta 92F, later the 92FS....

 and M16A2 for select troops) in 1994, it was used with great success in the Balkans and in more recent conflicts, including the Afghanistan
War in Afghanistan (2001–present)
The War in Afghanistan began on October 7, 2001, as the armed forces of the United States of America, the United Kingdom, Australia, and the Afghan United Front launched Operation Enduring Freedom...

 and Iraq theaters. The M4 carbine has a three-round burst
Burst mode (firearm)
In automatic firearms, burst mode or burst fire is a firing mode enabling the shooter to fire a predetermined number of rounds, usually 2 or 3 rounds and 100+ on anti-aircraft weapons, with a single pull of the trigger. This firing mode is commonly used in submachine guns, assault rifles and carbines...

 firing mode, while the M4A1 carbine has a fully automatic
Automatic firearm
An automatic firearm is a firearm that loads another round mechanically after the first round has been fired.The term can be used to refer to semi-automatic firearms, which fire one shot per single pull of the trigger , or fully automatic firearms, which will continue to load and fire ammunition...

 firing mode. Both have a Picatinny rail
Picatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...

 on the upper receiver, allowing the carry handle/rear sight assembly to be replaced with other sighting devices.

C7 and C8

The Diemaco
Diemaco
Diemaco was a Canadian defense company based in Kitchener, Ontario, Canada, that manufactured the C7 family of rifles under a licence from Colt. It was acquired by Colt on May 20, 2005, in a $18.2 million purchase from parent company Héroux-Devtek Inc, which had purchased Diemaco in 2000....

 C7 and C8 are updated variants of the M16 developed and used by the Canadian Forces
Canadian Forces
The Canadian Forces , officially the Canadian Armed Forces , are the unified armed forces of Canada, as constituted by the National Defence Act, which states: "The Canadian Forces are the armed forces of Her Majesty raised by Canada and consist of one Service called the Canadian Armed Forces."...

 and are now manufactured by Colt Canada
Colt Canada
Colt Canada is a firearms manufacturer owned by US based Colt and located in Kitchener, Ontario, Canada.The company is a defense contractor that manufactures and supplies small arms to the Canadian Forces and Canadian law enforcement agencies, as well as defense research & development, training,...

. The C7 is a further development of the experimental M16A1E1. Like earlier M16s, it can be fired in either single shot or automatic mode, instead of the burst function selected for the M16A2. The C7 also features the structural strengthening, improved handguards, and longer stock developed for the M16A2. Diemaco changed the trapdoor in the buttstock to make it easier to access and a spacer of 0.5 inches (12.7 mm) is available to adjust stock length to user preference. The most easily noticeable external difference between American M16A2s and Diemaco C7s is the retention of the A1 style rear sights. Not easily apparent is Diemaco's use of hammer-forged barrels. The Canadians originally desired to use a heavy barrel profile instead.

The C7 has been developed to the C7A1, with a Weaver rail on the upper receiver for a C79 optical sight, and to the C7A2, with different furniture and internal improvements. The Diemaco produced Weaver rail on the original C7A1 variants does not meet the M1913 'Picatinny' standard, leading to some problems with mounting commercial sights. This is easily remedied with minor modification to the upper receiver or the sight itself. Since Diemaco's acquisition by Colt to form Colt Canada, all Canadian produced flattop upper receivers are machined to the M1913 standard.

The C8 is the carbine version of the C7. The C7 and C8 are also used by Hærens Jegerkommando
Hærens Jegerkommando
Hærens Jegerkommando is a special forces unit of the Norwegian military. It is the armed forces competence center for commando, airborne and counter terrorist duty in the Norwegian Army. Its headquarters are located 30 km...

, Marinejegerkommandoen
Marinejegerkommandoen
Marinejegerkommandoen is a Norwegian maritime special forces unit. It was formally established in 1951. It is located in Ramsund in the northern part of Norway and at Haakonsvern Naval Base in Bergen...

 and FSK (Norway), Military of Denmark
Military of Denmark
The armed forces of the Kingdom of Denmark, known as the Danish Defence is charged with the defence of the Kingdom of Denmark.The Chief of Defence is the head of the Danish Armed Forces, and is head of the Defence Command which is managed by the Ministry of Defence. Constitutionally, the...

 (all branches), the Royal Netherlands Army
Royal Netherlands Army
The Royal Netherlands Army is the land forces element of the military of the Netherlands.-Short history:The Royal Netherlands Army was raised on 9 January 1814, but its origins date back to 1572, when the so-called Staatse Leger was raised...

 and Netherlands Marine Corps
Netherlands Marine Corps
The Korps Mariniers is the marine corps and amphibious infantry component of the Royal Netherlands Navy. The marines are trained to operate anywhere in the world in all environments, under any condition and circumstance, as a rapid reaction force. The Korps Mariniers can be deployed to a given...

 as its main infantry weapon. Following trials, variants became the weapon of choice of the British SAS
Special Air Service
Special Air Service or SAS is a corps of the British Army constituted on 31 May 1950. They are part of the United Kingdom Special Forces and have served as a model for the special forces of many other countries all over the world...

.

Others

  • The Chinese Norinco CQ
    Norinco CQ
    The CQ is a copy of the Colt M16 rifle. It is currently being manufactured by Norinco. According to the Norinco website, the rifle is officially known as CQ 5.56.-History:...

     is an unlicensed derivative of the M16A1 made specifically for export, with the most obvious external differences being in its handguard and revolver
    Revolver
    A revolver is a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing. The first revolver ever made was built by Elisha Collier in 1818. The percussion cap revolver was invented by Samuel Colt in 1836. This weapon became known as the Colt Paterson...

    -style pistol grip.

  • Khaybar KH2002
    Khaybar KH2002
    Khaybar/KH-2002 is an Iranian designed assault rifle, derived from the DIO S 5.56 assault rifle and further developed by Iran's Defense Industries Organization...

    , is an Iran
    Iran
    Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

    ian bullpup
    Bullpup
    Bullpups are firearm configurations in which the action is located behind the trigger group and alongside the shooter's face, so there is no wasted space for the buttstock as in conventional designs. This permits a shorter firearm length for the same barrel length for improved maneuverability, and...

     conversion of the locally produced S-5.56 rifle. Iran intends to replace the standard issue weapon of its armed forces with the Khaybar. The S-5.56 assault rifle itself is an Iranian M16 derivative based on the Norinco CQ. Two versions of the S-5.56 include the S-5.56A1, used for M-193-type bullets while the S-5.56A3 is used for SS-109-type bullets.

  • The MSSR rifle
    MSSR rifle
    The Marine Scout Sniper Rifle or MSSR is a semi-automatic sniper rifle developed from the Colt M16A1 rifle by the Philippine Marine Corps Scout Snipers due to the lack of a dedicated sniper rifle which is used in the Armed Forces of the Philippines....

     developed as an effective, low cost sniper rifle by the Philippine Marine Corps
    Philippine Marine Corps
    The Philippine Marine Corps is the marine corps of the Philippines, and is part of the Philippine Navy.- History :...

     Scout Snipers. The Special Operations Assault Rifle (SOAR)
    Special Operations Assault Rifle (SOAR)
    Special Operations Assault Rifle is an assault rifle manufactured by the Philippine-based company Ferfrans and designed as an improvement of the M16A1, AR-15 and M4 rifles.-Details:...

     assault carbine was developed by Ferfrans
    Ferfrans
    Ferfrans Specialties is a firearms and ammunition manufacturer based in Cebu, the Philippines.It provides weapons for the Philippine National Police and the Armed Forces of the Philippines....

     based on the M16 rifle. It is used by the Special Action Force
    Special Action Force
    The Special Action Force is the National Mobile Unit of the Philippine National Police. It is formed along the lines of the British Army Special Air Service, but with different recruitment and selection procedures...

    .

  • Taiwan
    Republic of China Army
    The ROC Army's current operational strength includes 3 armies, 5 corps. As of 2005, the Army's 35 brigades include 25 infantry brigades, 5 armoured brigades and 3 mechanized infantry brigades...

     uses piston-driven M16-based weapons as their standard rifle. These include the T65, T86
    T86 assault rifle
    The T86 assault rifle is a gas-operated, magazine-fed, air-cooled assault rifle. It is the second original rifle design conducted by the 205th Armory of Combined Service Forces, Republic of China...

     and T91 assault rifle
    T91 assault rifle
    The T91 assault rifle is produced by the 205th Armory, Ministry of Defense, Republic of China . It is based on the proven T86 assault rifle incorporating features from the M16 and AR-18 rifles with more modern features...

    s.

Summary

Colt model no. Military designation Barrel Length Barrel Handguard type Buttstock type Pistol grip type Lower receiver type Upper receiver type Rear sight type Front sight type Muzzle device Forward assist? Case deflector? Bayonet lug? Trigger pack
601 AR-15 20 in (508 mm) A1 profile (1:14 twist) Green or brown full-length triangular Green or brown fixed A1 A1 A1 A1 A1 A1 Duckbill flash suppressor No No Yes Safe-Semi-Auto
602 AR-15 or XM16 20 in (508 mm) A1 profile (1:12 twist) Full-length triangular Fixed A1 A1 A1 A1 A1 A1 Duckbill or three-prong flash suppressor No No Yes Safe-Semi-Auto
603 XM16E1 20 in (508 mm) A1 profile (1:12 twist) Full-length triangular Fixed A1 A1 A1 A1 A1 A1 Three-prong or M16A1 birdcage flash suppressor Yes No Yes Safe-Semi-Auto
603 M16A1 20 in (508 mm) A1 profile (1:12 twist) Full-length triangular Fixed A1 A1 A1 A1 A1 A1 M16A1-style birdcage flash suppressor Yes No Yes Safe-Semi-Auto
604 M16 20 in (508 mm) A1 profile (1:12 twist) Full-length triangular Fixed A1 A1 A1 A1 A1 A1 Three-prong or M16A1-style birdcage flash suppressor No No Yes Safe-Semi-Auto
645 M16A1E1/PIP 20 in (508 mm) A2 profile (1:7 twist) Full-length ribbed Fixed A2 A1 A1 or A2 A1 or A2 A1 or A2 A2 M16A1 or M16A2-style birdcage flash suppressor Yes Yes or No Yes Safe-Semi-Auto or Safe-Semi-Burst
645 M16A2 20 in (508 mm) A2 profile (1:7 twist) Full-length ribbed Fixed A2 A2 A2 A2 A2 A2 M16A2-style birdcage flash suppressor Yes Yes Yes Safe-Semi-Burst
645E M16A2E1 20 in (508 mm) A2 profile (1:7 twist) Full-length ribbed Fixed A2 A2 A2 Flattop with Colt Rail Flip-up Folding M16A2-style birdcage flash suppressor Yes Yes Yes Safe-Semi-Burst
N/A M16A2E2 20 in (508 mm) A2 profile (1:7 twist) Full-length semi-beavertail w/ HEL guide Retractable ACR ACR A2 Flattop with Colt rail None A2 ACR muzzle brake Yes Yes Yes Safe-Semi-Burst
646 M16A2E3/M16A3 20 in (508 mm) A2 profile (1:7 twist) Full-length ribbed Fixed A2 A2 A2 A2 A2 A2 M16A2-style birdcage flash suppressor Yes Yes Yes Safe-Semi-Auto
655 M16A1 Special High Profile 20 in (508 mm) HBAR profile (1:12 twist) Full-length triangular Fixed A1 A1 A1 A1 A1 A1 M16A1-style birdcage flash suppressor Yes No Yes Safe-Semi-Auto
656 M16A1 Special Low Profile 20 in (508 mm) HBAR profile (1:12 twist) Full-length triangular Fixed A1 A1 A1 A1 with modified Weaver base Low Profile A1 Hooded A1 M16A1-style birdcage flash suppressor Yes No Yes Safe-Semi-Auto
945 M16A2E4/M16A4 20 in (508 mm) A2 profile (1:7 twist) Full-length ribbed or KAC M5 RAS Fixed A2 A2 A2 Flattop with MIL-STD-1913 rail None A4 M16A2-style birdcage flash suppressor Yes Yes Yes Safe-Semi-Burst
Colt model no. Military designation Barrel Length Barrel Handguard type Buttstock type Pistol grip type Lower receiver type Upper receiver type Rear sight type Front sight type Muzzle device Forward assist? Case deflector? Bayonet lug? Trigger pack

Production and users

The M16 is the most commonly manufactured 5.56x45 mm rifle in the world. Currently, the M16 is in use by 15 NATO countries and more than 80 countries world wide. Together, numerous companies in the United States, Canada, and China have produced more than 8,000,000 rifles of all variants. Approximately 90% are still in operation. The M16 replaced the M14
M14 rifle
The M14 rifle, formally the United States Rifle, 7.62 mm, M14, is an American selective fire automatic rifle firing 7.62x51mm NATO  ammunition. It was the standard issue U.S. rifle from 1959 to 1970. The M14 was used for U.S...

 and M1 carbine
M1 Carbine
The M1 carbine is a lightweight, easy to use semi-automatic carbine that became a standard firearm for the U.S. military during World War II, the Korean War and the Vietnam War, and was produced in several variants. It was widely used by U.S...

 as standard infantry rifles of the U.S. armed forces. The M14 continues to see limited service, mostly in sniper
Sniper
A sniper is a marksman who shoots targets from concealed positions or distances exceeding the capabilities of regular personnel. Snipers typically have specialized training and distinct high-precision rifles....

, designated marksman
Designated marksman
The designated marksman is a military marksman role in a U.S. infantry squad. The term sniper was used in Soviet doctrine although the soldiers using the Dragunov were the first to use a specifically designed designated marksman's rifle. Sniper is also used in Russian doctrine...

, and ceremonial roles.

Users

Used M16A1 in the Falklands. Currently uses the M16A2. (M16A1) (Replaced 1989 by the F88 AuSteyr
Steyr AUG
The AUG is an Austrian bullpup 5.56mm assault rifle, designed in the early 1970s by Steyr Mannlicher GmbH & Co KG . The AUG was adopted by the Austrian Army as the StG 77 in 1977, where it replaced the 7.62mm StG 58 automatic rifle...

): Used by the military, special forces and counter terrorism units. (M16A1): C7 and C8 variants made by Colt Canada
Colt Canada
Colt Canada is a firearms manufacturer owned by US based Colt and located in Kitchener, Ontario, Canada.The company is a defense contractor that manufactures and supplies small arms to the Canadian Forces and Canadian law enforcement agencies, as well as defense research & development, training,...

 is used by the Canadian Forces
Canadian Forces
The Canadian Forces , officially the Canadian Armed Forces , are the unified armed forces of Canada, as constituted by the National Defence Act, which states: "The Canadian Forces are the armed forces of Her Majesty raised by Canada and consist of one Service called the Canadian Armed Forces."...

.: C7 and C8 variants made by Colt Canada are used by the Royal Danish Army
Royal Danish Army
The Royal Danish Army is the land warfare branch of the Danish Defence Forces, together with the Danish Home Guard.For the last decade, the Royal Danish Army has undergone a massive transformation of structures, equipment and training methods, abandoning its traditional role of anti-invasion...

. (M16A1-M16A2) M16A2/M4 is used by the Special forces of the Hellenic Army
Hellenic Army
The Hellenic Army , formed in 1828, is the land force of Greece.The motto of the Hellenic Army is , "Freedom Stems from Valor", from Thucydides's History of the Peloponnesian War...

 ISAF Forces in Afghanistan ] and Hellenic Navy
Hellenic Navy
The Hellenic Navy is the naval force of Greece, part of the Greek Armed Forces. The modern Greek navy has its roots in the naval forces of various Aegean Islands, which fought in the Greek War of Independence...

 (M-16A1) Indonesian Army
Indonesian Army
The Indonesian Army , the land component of the Indonesian Armed Forces, has an estimated strength of 328,517 regular personnel. The force's history began in 1945 when the Tentara Keamanan Rakyat "Civil Security Forces" served as paramilitary and police.Since the nation's independence struggle,...

 largely used M16s during Indonesian invasion of East Timor. Now used by Indonesian Special Forces.: Iraqi army
Iraqi Army
The Iraqi Army is the land component of the Iraqi military, active in various forms since being formed by the British during their mandate over the country after World War I....

.: During Vietnam War
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 provided 27,000 M16 rifles to Republic of Korea Armed Forces in Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

. Also, 600,000 Units were manufactured under license by Daewoo
Daewoo
Daewoo or the Daewoo Group was a major South Korean chaebol . It was founded on 22 March 1967 as Daewoo Industrial and was dismantled by the Korean government in 1999...

. The delivery started in 1974 and ended in 1985.: Lithuanian Armed Forces. (Replaced 1988 by Steyr AUG): C7 and C8 variants are used by the Royal Netherlands Army
Royal Netherlands Army
The Royal Netherlands Army is the land forces element of the military of the Netherlands.-Short history:The Royal Netherlands Army was raised on 9 January 1814, but its origins date back to 1572, when the so-called Staatse Leger was raised...

.: Special Service Group (SSG) of the Pakistan Army
Pakistan Army
The Pakistan Army is the branch of the Pakistani Armed Forces responsible for land-based military operations. The Pakistan Army came into existence after the Partition of India and the resulting independence of Pakistan in 1947. It is currently headed by General Ashfaq Parvez Kayani. The Pakistan...

. (M16A1): Manufactured under license by Elisco Tool and Manufacturing.: Local variant of the M16A1 (M16S1) manufactured under license by ST Kinetics. (M16A1/A2/A4) (M16A1/A2/A4): Special Air Service
Special Air Service
Special Air Service or SAS is a corps of the British Army constituted on 31 May 1950. They are part of the United Kingdom Special Forces and have served as a model for the special forces of many other countries all over the world...

. (M16A1, captured)


Future replacement

Previous attempts by the U.S. Military to replace the M16 were unsuccessful or only supplemented it. The M4 carbine will eventually replace the M16 rifle in the United States Army.

Background

Throughout the 1970s, the Army experimented with various materials to replace brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

 in cartridge casings. Brass has a number of qualities that make it almost ideal for a cartridge, including low friction against steel, making it easier to extract, and the ease with which casings can be manufactured. However, brass is also dense and expensive, so replacing it could lower both the cost and weight of the ammunition.

Aluminum and steel were popular materials for complete rounds, and AAI successfully developed a plastic blank. Completely caseless ammunition was also studied on several occasions, notably the German 4.7 mm designs, and this concept is now being continued with the Lightweight Small Arms Technologies
Lightweight Small Arms Technologies
The Lightweight Small Arms Technologies program is funded by the U.S. Joint Service Small Arms Program, with the goal of significantly reducing the weight of small arms and their ammunition...

 Program.

Later in the 1980s, the Advanced Combat Rifle
Advanced Combat Rifle
The Advanced Combat Rifle was a United States Army program to find a replacement for the M16 assault rifle. The program's total cost is approximately US$300 million...

 program was run to find a replacement for the M16. Colt entered a modified M16A2 known as the Colt ACR, which used duplex rounds, a system that lowered recoil by 40% to improve repeating shots, and added a 3.5x scope. This weapon, designated M16A2E2, also featured a "guide" of sorts as part of a special handguard developed by the U.S. Army Human Engineering Laboratory designed to assist in snap-shooting, and a carbine style stock very similar to the recent stock developed by the Naval Surface Warfare Center Crane Division
Naval Surface Warfare Center Crane Division
Naval Surface Warfare Center Crane Division is the principal tenant command located at Naval Support Activity Crane. NSA Crane is a United States Navy installation located approximately southwest of Bloomington, Indiana and predominantly located in Martin County, but small parts also extend into...

.

The Steyr ACR
Steyr ACR
The Steyr ACR was a prototype flechette-firing assault rifle built for the US Army's Advanced Combat Rifle program of 1989/90. Although the Steyr design proved effective, as did most of the weapons submitted, the entire ACR program ended with none of the entrants achieving performance 100% better...

 used new flechette ammunition that was nominally called 5.56 mm, with a very high 4750 ft/s (1,448 m/s) muzzle velocity. Other variants experimented with caseless ammunition
Caseless ammunition
Caseless ammunition is a type of small arms ammunition that eliminates the cartridge case that typically holds the primer, propellant, and projectile together as a unit...

 technologies as well.

Replacement designs

In the 1980s, the M249
M249 light machine gun
The M249 light machine gun , previously designated the M249 Squad Automatic Weapon , and formally written as Light Machine Gun, 5.56 mm, M249, is an American version of the Belgian FN Minimi, a light machine gun manufactured by the Belgian company FN Herstal . The M249 is manufactured in the...

 was issued to infantry units, replacing some M60
M60 machine gun
The M60 is a family of American general-purpose machine guns firing 7.62×51mm NATO cartridges from a disintegrating belt of M13 links...

s and some M16A1s at the squad level. In the 1990s the M4 carbine
M4 carbine
The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 designed by Eugene Stoner and made by ArmaLite. It is a shorter and lighter variant of the M16A2 assault rifle, with 80% parts commonality.It is a gas-operated,...

 took over the operational role of the M3 submachine gun
M3 submachine gun
The M3 was an American .45-caliber submachine gun adopted for U.S. Army service on 12 December 1942, as the United States Submachine Gun, Cal. .45, M3. The M3 was designed as a more cost-effective alternative to the Thompson, optimized for mass production...

, some M9s
M9 Pistol
The Beretta M9, formally Pistol, Semiautomatic, 9mm, M9, is a 9×19mm Parabellum pistol of the United States military adopted in 1985. It is essentially a military specification Beretta 92F, later the 92FS....

, and many M16A2s. The U.S. Air Force mostly uses M4 and GAU-5 carbines for security squadrons and M16A2s for non-security personnel. The U.S. Navy decided to retain the M16A2 and M16A3 for its units that use rifles like the U.S. Navy Seabees. The U.S. Army and Marine Corps have largely relegated the M16A2 to non-combat roles, choosing instead the M16A4 and M4. Further, the M16 never entirely replaced the M14 in all roles, which continues to be used in a number of niche applications throughout the Armed Forces, especially with the U.S. Navy.

Replacement of the M16 family has been proposed at various points, and its longevity is in part due to a series of failures in projects meant to replace it, driven largely by the requirement for a significant improvement. Immediately after the introduction of the M16, the Marine Corps sought to adopt the Stoner 63
Stoner 63
The Stoner 63, also known as the XM22/E1, is an American modular weapons system designed by Eugene Stoner in the early 1960s. It was produced by Cadillac Gage and used in very limited numbers in Vietnam by members of the United States Navy SEALs and several law enforcement...

. Although they found it superior in most ways, it was still at an early stage of development; the Marines chose the technically inferior but mature M16. The Advanced Combat Rifle
Advanced Combat Rifle
The Advanced Combat Rifle was a United States Army program to find a replacement for the M16 assault rifle. The program's total cost is approximately US$300 million...

 program in the 1980s produced weapons that were superior in some ways, but none improved upon the M16 series enough to replace it. It was also potentially going to be replaced by the SABR, from the OICW
Objective Individual Combat Weapon program
The Objective Individual Combat Weapon or OICW was the next-generation service rifle competition that was under development as part of the United States Army OICW program; the program was eventually discontinued without bringing the weapon out of the prototype phase...

 project. The weapon system originally planned by the OICW project was put on hold around the turn of century, in favor of a simpler new 5.56 mm rifle project that offered less far-reaching improvements. The resulting XM8 rifle
XM8 rifle
The XM8 was a developmental U.S. Military designation and project name for a lightweight assault rifle system that was under development by the United States Army from the late 1990s to early 2000s...

 was also intended as a potential replacement for the M16 family. However, this program too ran into problems around 2004–05, and was put on hold in favor of an open competition for what became known as the OICW Increment 1. (Increment 2 is the standalone XM25 Individual Airburst Weapon System, and Increment 3 is the XM29 OICW
XM29 OICW
The XM29 OICW was a series of prototypes of a new type of battle rifle that fired 20 mm HE airbursting projectiles. The prototypes were developed as part of the Objective Individual Combat Weapon program in the 1990s...

, a weapon that combined the earlier two increments.) This competition was subsequently put on hold in the summer of 2005 to take into account input from other services, and on October 31, 2005, the competition was canceled.

A partial replacement for the M16 rifle is the SOF Combat Assault Rifle (SCAR
FN SCAR
The Special Operations Forces Combat Assault Rifle, or SCAR, is a modular rifle made by FN Herstal for the United States Special Operations Command to satisfy the requirements of the SCAR competition. This family of rifles consist of two main types...

), designated Mk 16. The 5.56x45 Mk 16 emerged as the winner of a USSOCOM competition to find a new rifle for Special Operations Forces in 2003. Most of the SCAR's basic controls (pistol grip, magazine release, selector lever, and bolt release) share the same location and function as on the M16 and M4 they are supplementing.

Since the cancellation of the XM8 program, and into 2008, the LSAT rifle
LSAT rifle
The LSAT rifle, of the LSAT program, is a developmental assault rifle. Design began in 2008, four years after the beginning of the LSAT program. Like the LSAT LMG, the rifle is designed to be significantly lighter than existing designs, and is designed to fire lighter ammunition...

 program has been pursued for the next generation of U.S. small arms
Small arms
Small arms is a term of art used by armed forces to denote infantry weapons an individual soldier may carry. The description is usually limited to revolvers, pistols, submachine guns, carbines, assault rifles, battle rifles, multiple barrel firearms, sniper rifles, squad automatic weapons, light...

. The program has already produced practical results and is currently projected to provide the next U.S. military rifle. Development of the LSAT rifle began in 2008.

Several companies have been working on and creating potential candidates for the U.S. Army's next primary weapon. The Heckler & Koch HK416 has been in use by Delta Force
Delta Force
1st Special Forces Operational Detachment-Delta is one of the United States' secretive Tier One counter-terrorism and Special Mission Units. Commonly known as Delta Force, Delta, or The Unit, it was formed under the designation 1st SFOD-D, and is officially referred to by the Department of Defense...

 since 2004. The HK416 is offered as a conversion kit that can retrofit
Retrofit
Retrofitting refers to the addition of new technology or features to older systems.* power plant retrofit, improving power plant efficiency / increasing output / reducing emissions...

 current M4 carbines. The HK416 recently won a testing competition for the US Marine Corps Infantry Automatic Rifle program and entered final testing as the M27 in summer 2010. The HK416 is also one of several M4 designs on the front competitors of the Army's Individual Carbine competition. The H&K's design replaces the direct impingement gas system with a newer piston design. The reason to build a new M4 is to produce a new more reliable carbine for US troops in a few years. However in November 2011 leaders of the US Marine Corps announced they will stay with current M-4 Carbines and M-16A4s and not adopt a ICC competition winner. The USMC is considering upgrading the M-16A4. http://www.military.com/news/article/marines-wont-follow-armys-lead-on-new-carbine.html?col=1186032325324

During the late 1990s and early 2000s the IMI developed the IMI Tavor TAR-21
IMI Tavor TAR-21
The TAR-21 is an Israeli bullpup assault rifle chambered for 5.56×45mm NATO ammunition with a selective fire system, selecting between semi-automatic mode, burst mode, and full automatic fire mode. It is named after Mount Tavor, while "TAR-21" stands for "Tavor Assault Rifle - 21st Century". It is...

 which has supplemented the M16s and M4s in service with the Israeli Defense Force.

The M4 carbine will eventually replace the M16 rifle in most combat units in the U.S. Army.

Gas Piston

Complicating the Army search for higher reliability in the M4 is a number of observations of M4 gas piston alternatives that suffer unintended design problems. The first is that many of the gas piston modifications for the M4 isolate the piston so that piston jams or related malfunction require the entire weapon be disassembled, such disassembly cannot be performed by the end user and requires a qualified armorer to perform out of field, where as any malfunction with the direct-impingement system can be fixed by the end user in field. The second is that gas piston alternatives use an off-axis operation of the piston that can introduce carrier tilt, whereby the bolt carrier fails to enter the buffer tube at a straight angle resulting in part wearing. The third is that the use of a sound suppressor results in hot gases entering the chamber, regardless of a direct-gas impingement or gas piston design choice.

See also

  • AR-15 variants
    AR-15 variants
    This article is a review of many variations of the AR-15 family of weapons. Weapons patterned on the original ArmaLite AR-15 have been produced by numerous manufacturers and have been used by nations around the world, some of which created their own variations. The tables here are split in a...

     – list of all AR-15 and M16 variants
  • Winchester LMR
    Winchester LMR
    The Winchester LMR is a prototype rifle that was developed for military use but was sidelined in 1964 by the AR-15....

  • M203 40 mm grenade launcher
    M203 grenade launcher
    The M203 is a single shot 40 mm grenade launcher designed to attach to a rifle. It uses the same rounds as the older M79 break-action grenade launcher, which utilize the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was...

  • Colt 9mm SMG
    Colt 9mm SMG
    The Colt 9mm SMG is a 9x19mm Parabellum submachine gun manufactured by Colt, based on the M16 rifle platform.-Design details:The Colt 9mm SMG is a closed bolt, blowback operated SMG, rather than the conventional direct impingement gas operation of the standard 5.56x45mm M16 type rifle.The overall...

  • Comparison of the AK-47 and M16
    Comparison of the AK-47 and M16
    Two of the most common assault rifles in the world are the AK-47 and the M16. They have faced each other in countless conflicts both large and small, and have spawned comparisons and controversy since the early 1960s.- Influence of World War II :...

  • List of individual weapons of the U.S. armed forces
  • Adaptive Combat Rifle
    Adaptive Combat Rifle
    The Adaptive Combat Rifle is the production name for an updated version of the Masada Adaptive Combat Weapon System. In late January 2008, Bushmaster entered into a licensing agreement with Magpul whereby Bushmaster would take over production, future development and sales of the Masada...

  • Daewoo K2
    Daewoo K2
    The Daewoo Precision Industries K2 is an assault rifle of the Republic of Korea Armed Forces, manufactured by Daewoo Precision Industries. It is a shoulder-fired, gas-operated, selective-fire assault rifle that feeds from a 20 or 30 round magazine and is chambered for 5.56 NATO. The K2 replaced the...

    , Republic of Korea Armed Forces (South Korea) assault rifle
  • Robinson Arms XCR
    Robinson Arms XCR
    The Robinson Armament Co. XCR is a multi-caliber, gas piston weapon system developed by Robinson Armament Co. for U.S. Special Operations Command to satisfy the requirements of the SOF Combat Assault Rifle, or SCAR competition, but was disqualified on a technicality due to late delivery of blank...

  • T65 assault rifle, AR-15 variant developed by ROC Army
    Republic of China Army
    The ROC Army's current operational strength includes 3 armies, 5 corps. As of 2005, the Army's 35 brigades include 25 infantry brigades, 5 armoured brigades and 3 mechanized infantry brigades...

  • Norinco CQ
    Norinco CQ
    The CQ is a copy of the Colt M16 rifle. It is currently being manufactured by Norinco. According to the Norinco website, the rifle is officially known as CQ 5.56.-History:...

    , M16 clone developed by China
    China
    Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

    .
  • MSBS Radon
    MSBS Radon
    MSBS "Radon" is an assault rifle currently under development as a future service rifle of the Polish Army. There are two basic variants under development currently: a bullpup version and a standard version with folding, retractable stock...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK