M4 Carbine
Overview
 
The M4 carbine is a family of firearms tracing its lineage back to earlier 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....

 versions of the M16
M16 rifle
The M16 is the United States military designation for the AR-15 rifle adapted for both semi-automatic and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO...

, all based on the original 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....

 designed by 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...

 and made by 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...

. It is a shorter and lighter variant of the M16A2
M16 rifle
The M16 is the United States military designation for the AR-15 rifle adapted for both semi-automatic and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO...

 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 80% parts commonality.

It is a 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...

, air-cooled, magazine-fed, selective fire, shoulder-fired weapon with a telescoping stock. A shortened variant of the M16A2 rifle, the M4 has a 14.5 in (368.3 mm) barrel, allowing its user to better operate in close quarters combat.
Encyclopedia
The M4 carbine is a family of firearms tracing its lineage back to earlier 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....

 versions of the M16
M16 rifle
The M16 is the United States military designation for the AR-15 rifle adapted for both semi-automatic and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO...

, all based on the original 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....

 designed by 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...

 and made by 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...

. It is a shorter and lighter variant of the M16A2
M16 rifle
The M16 is the United States military designation for the AR-15 rifle adapted for both semi-automatic and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO...

 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 80% parts commonality.

It is a 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...

, air-cooled, magazine-fed, selective fire, shoulder-fired weapon with a telescoping stock. A shortened variant of the M16A2 rifle, the M4 has a 14.5 in (368.3 mm) barrel, allowing its user to better operate in close quarters combat. The M4 has selective fire
Selective fire
A selective fire firearm has at least one semi–automatic and one automatic mode, which is activated by means of a selector which varies depending on the weapon's design. Some selective fire weapons utilize burst fire mechanisms to limit the maximum or total number of shots fired automatically in...

 options including semi-automatic
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...

 and 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...

 (like the M16A4), while the M4A1 has the capability to fire 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...

 instead of three-round burst. The carbine is also capable of mounting an 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 M203A1 with a 9-inch barrel as opposed to the standard 12-inch barrel of the M203 used on the M16 series.

The M4 carbine is heavily used by the U.S military. It is slated to eventually replace the M16 rifle for most combat units in the United States Army. The winner of the Individual Carbine competition may replace the M4 carbine in U.S. Army service.

History

The M4 was intended to replace selected M9 pistols and M16 rifle series with most Army units (this plan was thought to be changed with the development of 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...

 and the XM8 carbine
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...

; however, both projects were canceled.)

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...

 has ordered its officers (up to the rank of lieutenant colonel) and Staff Non-commissioned officers to carry the M4 carbine instead of the 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....

 handgun. This is in keeping with the Marine Corps doctrine, "Every Marine a rifleman." The Marines however chose the full-sized M16A4 over the M4 as its standard infantry rifle. 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...

 corpsmen E5 and below will also be issued M4s instead of the M9.

Improved M4

On July 1, 2009, the U.S. Army took complete ownership of the M4 design. This will allow companies besides Colt to compete with their own M4 designs. The Army planned on fielding the last of its M4 requirement in 2010. On October 30, 2009, Army weapons officials proposed a series of changes to the M4 to Congress. Requested changes include an electronic round counter that records the number of shots fired, a heavier barrel, and possibly replacing the 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 :...

 system with a gas piston system, the benefits of this, however, have come under scrutiny from both the military and civilian firearms community. It should also be pointed out that, according to a PDF detailing the M4 Carbine improvement plans released by PEO Soldier, the direct impingement system will only be replaced after reviews are done comparing the direct impingement system to commercial gas piston operating system to find out and use the best available operating system in the US Army's improved M4A1.

As of September 2010 the Army has announced it will buy 12,000 M4A1s from Colt Firearms by the end of 2010 and will by early 2011 order 25,000 more M4A1s. The Army announced also to have open competition for the newly designed M4 bolt carrier and gas piston operation system, which will be fitted to the newly bought M4A1 carbines. The service branch plans to buy 12,000 of these conversion kits in early 2011. In late 2011 the Army plans to buy 65,000 more conversion kits. From there the Army will decide if it will upgrade all of its M4s.

Future replacement

The carbine variant of the 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 canceled in 2005.

On November 13, 2008, the U.S. Army hosted an invitation-only Industry Day regarding a potential future replacement for the M4 carbine. Nineteen companies provided displays and briefings for military officials. The weapons displayed included the Barrett REC7 PDW, Bushmaster ACR, FN 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...

, Heckler & Koch HK416, Heckler & Koch XM8, LWRC M6A4, 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...

, SIG 556, as well as Colt's own improved version of the M4, the Colt ACC-M
Advanced Colt Carbine-Monolithic
The Advanced Colt Carbine-Monolithic is an improved version of the M4 carbine presented to the United States military at a conference as a possible replacement for the M16 rifle and M4 carbine within the military....

. The goal of the Industry Day was to provide officials with knowledge as to the current state of the art, which will assist the writing of a formal requirements document.

The possible successor to the M4 carbine in the U.S. Army is the Individual Carbine. This program is to provide a new carbine for the Army, while the USMC has decided to stay with the M4 for carbine use.

Design

The M4 and its variants fire 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...

 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 .223 Remington
.223 Remington
The .223 Remington is a sporting cartridge with almost the same external dimensions as the 5.56×45mm NATO military cartridge. The name is commonly pronounced either two-two-three or two-twenty-three. It is loaded with a diameter, jacketed bullet, with weights ranging from , though the most common...

 ammunition) and are gas-operated, air-cooled, 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, selective fire firearms with either a multi-position telescoping stock
Telescoping stock
A telescoping stock is a stock on a firearm that telescopes or folds in on itself in order to become more compact. Telescoping stocks are useful for storing a rifle or weapon in a space that it would not normally fit in. The user can either fold in the stock to make the weapon easier to handle, or...

 or a fixed A2 or LE tactical stock. Original M4 models had a flat-ended telescoping 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...

, but newer models are now equipped with a redesigned telescoping stock that is slightly larger with curvature at the end. The M4 is similar to much earlier compact M16 versions, such as the 1960s-era XM177 family. Some of those visual designs are obvious in both weapons, however most of the similarities are not very noticeable.

As with many 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....

s, the M4 is handy and more convenient to carry than a full-length rifle
Rifle
A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...

. The price is slightly inferior ballistic performance compared to the full-size M16, with its nearly 6" (15 cm) longer barrel. This becomes most apparent at ranges of 300 yards and beyond. Statistically, however, most small-arms engagements occur within 100 yards. This means that the M4 is very much an adequate weapon for the majority of troops. The marginal sacrifice in terminal ballistics
Terminal ballistics
Terminal ballistics, a sub-field of ballistics, is the study of the behavior of a projectile when it hits its target. It is often referred to as stopping power when dealing with human or other living targets. Terminal ballistics is relevant both for small caliber projectiles as well as for large...

 and range, in exchange for greatly improved handling characteristics, is usually thought to be a worthwhile compromise.

While the M4's maneuverability makes it a candidate for non-infantry
Infantry
Infantrymen are soldiers who are specifically trained for the role of fighting on foot to engage the enemy face to face and have historically borne the brunt of the casualties of combat in wars. As the oldest branch of combat arms, they are the backbone of armies...

 troops (vehicle crews, clerks and staff officers), it also makes it ideal for close quarters battle
Close quarters battle
Close quarters combat or close quarters battle is a type of fighting in which small units engage the enemy with personal weapons at very short range, potentially to the point of hand-to-hand combat or fighting with hand weapons such as swords or knives...

 (CQB). The M4 was developed and produced for the United States government
Federal government of the United States
The federal government of the United States is the national government of the constitutional republic of fifty states that is the United States of America. The federal government comprises three distinct branches of government: a legislative, an executive and a judiciary. These branches and...

 by Colt Firearms
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...

, which had an exclusive contract to produce the M4 family of weapons through 2009; however, a number of other manufacturers offer M4-like firearms. The M4, along with the M16A4, have mostly replaced the M16A2 in the Army and Marines. 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...

, for example, has transitioned completely to the M4 for Security Forces squadrons, while other armed personnel retain the M16A2. The US Navy uses M4A1s for Special Operations and by vehicle crews.

Some features of the M4 and M4A1 compared to a full-length M16-series rifle include:
  • Compact size
  • Shortened barrel 14.5 in (368.3 mm), which includes the shorter carbine gas system.
  • Telescoping buttstock


However, there have been some criticisms of the carbine, such as lower muzzle velocities
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...

 and louder report due to the shorter barrel, additional stress on parts because of the shorter gas system, and a tendency to overheat faster than the M16A2.

Accessories

Like all the variants of the M16, the M4 and the M4A1 can be fitted with many accessories, such as night vision devices, suppressors, laser pointers, telescopic sights, bipod
Bipod
A bipod is a support device that is similar to a tripod or monopod, but with two legs. It provides significant stability along two axes of motion .-Firearms:...

s, either the M203
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...

 or M320 grenade launchers, the M26 MASS shotgun,forward hand grips and anything else compatible with a MIL-STD-1913 Picatinny rail.

Other common accessories include the AN/PEQ-2
AN/PEQ-2
The AN/PEQ-2 Target Pointer/Illuminator/Aiming Light is a laser sight for use on rifles fitted with a Picatinny rail. It is manufactured by Insight Technology.The device is mil-spec and is currently in active service with the US armed forces...

, Advanced Combat Optical Gunsight
Advanced Combat Optical Gunsight
Advanced Combat Optical Gunsights are a series of telescopic sights manufactured by Trijicon. The ACOG is designed to be used on the M16 rifle and M4 carbine, but Trijicon has developed ACOG accessories for certain other firearms...

 (ACOG), and M68 CCO
Aimpoint CompM2
The CompM2 is a battery powered non-magnifying red dot type of reflex sight for firearms manufactured by Aimpoint AB. In the U.S. military, it is designated M68 Close Combat Optic and is also known as M68 Aimpoint and is designed to meet United States military standards...

. EOTech
EOTech
EOTech designs, manufactures, and markets electro-optic products and systems. The company is headquartered in Ann Arbor, Michigan. They produce holographic weapon sights for small arms that have been adopted by various military and law enforcement agencies as close quarters battle firearm...

 holographic weapon sights are part of the SOPMOD II package. Visible and IR (infrared) lights of various manufacturers are also commonly attached using various mounting methods. As with all versions of the M16, the M4 accepts a blank-firing attachment (BFA) for training purposes.

Feedramps

M4 feedramps are extended from the barrel extension into the upper receiver. This can help alleviate feeding problems which may occur as a result of the increased pressure of the shortened gas system of the M4. This problem is primarily seen in full-auto applications. While some feel they are unnecessary, their perceived or real utility to others has led to the increasing availability of this feature on civilian AR-15 products.

Variants

Except for the very first delivery order, all U.S. military-issue M4 and M4A1 carbines possess a flat-top NATO M1913-specification (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 top of the receiver
Receiver (firearms)
In firearms terminology, the receiver is the part of a firearm that houses the operating parts. The receiver usually contains the bolt carrier group, trigger group, and magazine port. In most handguns, the receiver, or frame, holds the magazine well or rotary magazine as well as the trigger mechanism...

 for attachment of optical sights and other aiming devices — Trijicon
Trijicon
Trijicon ) is an American company, based in Wixom, Michigan, that manufactures and distributes optical sighting devices for firearms, including pistols, rifles, and shotguns....

 TA01 and TA31 Advanced Combat Optical Gunsight
Advanced Combat Optical Gunsight
Advanced Combat Optical Gunsights are a series of telescopic sights manufactured by Trijicon. The ACOG is designed to be used on the M16 rifle and M4 carbine, but Trijicon has developed ACOG accessories for certain other firearms...

s (ACOG), EOTech 550 series
EOTech
EOTech designs, manufactures, and markets electro-optic products and systems. The company is headquartered in Ann Arbor, Michigan. They produce holographic weapon sights for small arms that have been adopted by various military and law enforcement agencies as close quarters battle firearm...

 holographic sights, and Aimpoint
Aimpoint AB
Aimpoint AB is a Swedish optics company manufacturing red dot sights for civilian, police and military use. The most popular model is the CompM2 , currently used by numerous armed forces around the world.- Company :...

 M68 Close Combat Optic
Aimpoint CompM2
The CompM2 is a battery powered non-magnifying red dot type of reflex sight for firearms manufactured by Aimpoint AB. In the U.S. military, it is designated M68 Close Combat Optic and is also known as M68 Aimpoint and is designed to meet United States military standards...

 (M68 CCO) being the favorite choices — and a detachable rail-mounted carrying handle. Standards are the Colt Model 920 (M4) and 921 (M4A1).

Variants of the carbine built by different manufacturers are also in service with many other foreign special forces units, such as the Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

n Special Air Service Regiment
Australian Special Air Service Regiment
The Special Air Service Regiment, officially abbreviated SASR but commonly known as the SAS, is a special forces unit of the Australian Army...

 (SASR). While the SASR uses weapons of essentially the same pattern built by Colt for export (Colt uses different models to separate weapons for the U.S. military and those for commercial/export purposes), 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...

 uses a variant on the basic theme, the 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,...

 (formerly 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....

) C8SFW.

The M4 carbine is slated to eventually replace the M16 rifle in the United States Army.

M4 MWS (Modular Weapon System)

Colt Model 925 carbines were tested fitted with the Knight's Armament Corporation (KAC) M4 RAS under the designation M4E2, but this designation appears to have been scrapped in favor of mounting this system to existing carbines without changing the designation. The U.S. Army Field Manual specifies for the Army that adding the Rail Adapter System (RAS) turns the weapon into the M4 MWS or Modular Weapon System.

M4A1

The M4A1 carbine is a fully automatic variant of the basic M4 carbine intended for special operations
Special forces
Special forces, or special operations forces are terms used to describe elite military tactical teams trained to perform high-risk dangerous missions that conventional units cannot perform...

 use. The M4A1 has a "S-1-F" (safe/semi-automatic/fully automatic) trigger group, while the M4 has a "S-1-3" (safe/semi-automatic/3-round burst) trigger group. The M4A1 is used by almost all U.S special operation units including, but not limited to, the Army Rangers
United States Army Rangers
United States Army Rangers are elite members of the United States Army. Rangers have served in recognized U.S. Army Ranger units or have graduated from the U.S. Army's Ranger School...

, Army Special Forces, Navy SEALs and Air Force Combat Control Teams. The M4A1 is especially favored by counter-terrorist
Counter-terrorism
Counter-terrorism is the practices, tactics, techniques, and strategies that governments, militaries, police departments and corporations adopt to prevent or in response to terrorist threats and/or acts, both real and imputed.The tactic of terrorism is available to insurgents and governments...

 and special forces
Special forces
Special forces, or special operations forces are terms used to describe elite military tactical teams trained to perform high-risk dangerous missions that conventional units cannot perform...

 units for close quarters combat because of the carbine's compactness and firepower. These features are also very useful in urban warfare
Urban warfare
Urban warfare is combat conducted in urban areas such as towns and cities. Urban combat is very different from combat in the open at both the operational and tactical level...

. It has a maximum effective range of about 500 to 600 m (546.8 to 656.2 yd).

All U.S. Army forces will begin replacing their basic M4 carbines and all 600,000 M16 rifles with the M4A1 variant in 2014. The M4A1 in turn would likely be replaced with the Individual Carbine. Replacement of the M16 would come from the Individual Carbine instead of the M4A1 if procurement was attained.

In the last few years, M4A1 carbines have been refit or received straight from factory with barrels with a thicker profile under the handguard. This is for a variety of reasons such as heat dissipation, which is useful due to the complaints of high-heat production from test soldiers, which occurs during full-auto and accuracy as a byproduct of barrel weight. These heavier barrel weapons are also fitted with a heavier buffer known as the H2. Out of three sliding weights inside the buffer, the H2 possesses two tungsten weights and one steel weight, versus the standard H buffer, which uses one tungsten weight and two steel weights. These weapons, known by Colt as the Model 921HB (for Heavy Barrel), have also been designated M4A1, and as far as the government is concerned the M4A1 represents both the 921 and 921HB.

Mark 18 CQBR

Current contractor for the Mark 18 is Colt and Lewis Machine & Tool (LMT) NSN 1005-01-527-2288. It is equipped with a 10.3" barrel.

SOPMOD Block I

USSOCOM
United States Special Operations Command
The United States Special Operations Command is the Unified Combatant Command charged with overseeing the various Special Operations Commands of the Army, Air Force, Navy and Marine Corps of the United States Armed Forces. The command is part of the Department of Defense...

 developed the Special Operations Peculiar Modification (SOPMOD
SOPMOD
The Special Operations Peculiar MODification kit is an accessory system for the M4A1 carbine and FN SCAR Mk 16/17 used by USSOCOM...

) Block I kit for the carbines used by units under its jurisdiction. The kit features an M4A1, a Rail Interface System (RIS) handguard developed by Knight's Armament Company, a shortened quick-detachable 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...

 and leaf sight
Sight (device)
A sight is a device used to assist aligning or aim weapons, surveying instruments, or other items by eye. Sights can be a simple set or system of markers that have to be aligned together as well as aligned with the target...

, a KAC sound suppressor
Suppressor
A suppressor, sound suppressor, sound moderator, or silencer, is a device attached to or part of the barrel of a firearm which reduces the amount of noise and flash generated by firing the weapon....

, a KAC back-up rear sight, an Insight Technologies AN/PEQ-2
AN/PEQ-2
The AN/PEQ-2 Target Pointer/Illuminator/Aiming Light is a laser sight for use on rifles fitted with a Picatinny rail. It is manufactured by Insight Technology.The device is mil-spec and is currently in active service with the US armed forces...

A visible 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...

/infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 designator, along with Trijicon's ACOG and Reflex sights
Red dot sight
A red dot sight is a common classification for a type of non-magnifying reflector sight for firearms that gives the user an aimpoint in the form of an illuminated red dot...

, and a night vision sight. This kit was designed to be configurable (modular) for various missions, and the kit is currently in service with special operations units.

SOPMOD Block II

A second-generation SOPMOD kit (now known as SOPMOD II) includes innovative optics, such as the Elcan Specter DR and the Eotech 553. Block II uses the RIS II rails manufactured by Daniel Defense in both a 9.5 and 12.5 length.

SOPMOD Block III

2012-XXXX
SOPMOD 1 & 2 Compatible with both M4A1 Carbine & SCAR
SOPMOD 2 Compatibilities with all SOF Weapons

2007 dust test

In the fall 2007, the Army tested the M4 against three other carbines in "sandstorm
Dust storm
A dust / sand storm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Particles are transported by saltation and suspension, causing soil to move from one place and deposition...

 conditions" at 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 :...

, Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

: the Heckler & Koch
Heckler & Koch
Heckler & Koch GmbH is a German defense manufacturing company that produces various small arms. Some of their products include the SA80, MP5 submachine gun, G3 automatic rifle, the G36 assault rifle, the HK 416, the MP7 personal defense weapon, the USP series of handguns, and the high-precision...

 XM8
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...

, 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....

 SOF Combat Assault Rifle
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...

 (SCAR) and the Heckler & Koch HK416. Ten of each type of rifle were used to fire 6,000 rounds each, for a total of 60,000 rounds per rifle type. The M4 suffered far more stoppages than its competitors: 882 stoppages, 19 requiring an armorer to fix. The XM8 had the fewest stoppages, 116 minor stoppages and 11 major ones, followed by the FN 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...

 with 226 stoppages and the HK416 with 233. The Army was quick to point out that even with 863 minor stoppages—termed "class one" stoppages which require 10 seconds or less to clear and "class two" stoppages which require more than ten seconds to clear—the M4 functioned well, with over 98 percent of the 60,000 total rounds firing without a problem. The Army said it planned to improve the M4 with a new cold-hammer-forged barrel to give longer life and more reliable magazines to reduce the stoppages. Magazine failures caused 239 of the M4's 882 failures. Army officials said the new magazines could be combat-ready by spring if testing went well.

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. The gas-piston system also causes the firearm to become proprietary to the manufacturer, making modifications and changes with parts from other manufacturers difficult. The argument for a gas piston is that it would reduce fouling; the argument against is that is would increase weight and reduce accuracy. The issue remains contentious and unresolved.

Trademark issues

Colt previously held a U.S. trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...

 on the term "M4". Many manufacturers have production firearms that are essentially identical to a military M4. Civilian models are sometimes colloquially referred to as "M4gery" (icon, a portmanteau of "M4" and "forgery"). Colt had maintained that it retains sole rights to the M4 name and design. Other manufacturers had long maintained that Colt had been overstating its rights, and that "M4" had now become a generic term for a shortened AR-15. In April 2004, Colt filed a lawsuit against Heckler & Koch
Heckler & Koch
Heckler & Koch GmbH is a German defense manufacturing company that produces various small arms. Some of their products include the SA80, MP5 submachine gun, G3 automatic rifle, the G36 assault rifle, the HK 416, the MP7 personal defense weapon, the USP series of handguns, and the high-precision...

 and Bushmaster Firearms, claiming acts of trademark infringement
Trademark infringement
Trademark infringement is a violation of the exclusive rights attaching to a trademark without the authorization of the trademark owner or any licensees...

, trade dress
Trade dress
Trade dress is a legal term of art that generally refers to characteristics of the visual appearance of a product or its packaging that signify the source of the product to consumers...

 infringement, trademark dilution
Trademark dilution
Trademark dilution is a trademark law concept giving the owner of a famous trademark standing to forbid others from using that mark in a way that would lessen its uniqueness. In most cases, trademark dilution involves an unauthorized use of another's trademark on products that do not compete with,...

, false designation of origin, false advertising
False advertising
False advertising or deceptive advertising is the use of false or misleading statements in advertising. As advertising has the potential to persuade people into commercial transactions that they might otherwise avoid, many governments around the world use regulations to control false, deceptive or...

, patent infringement
Patent infringement
Patent infringement is the commission of a prohibited act with respect to a patented invention without permission from the patent holder. Permission may typically be granted in the form of a license. The definition of patent infringement may vary by jurisdiction, but it typically includes using or...

, unfair competition
Unfair competition
Unfair competition in a sense means that the competitors compete on unequal terms, because favourable or disadvantageous conditions are applied to some competitors but not to others; or that the actions of some competitors actively harm the position of others with respect to their ability to...

, and deceptive trade practices. Heckler & Koch later settled out of court, changing one product's name from "HK M4" to "HK416". However, on December 8, 2005, a District court judge in Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

 granted a summary judgment
Summary judgment
In law, a summary judgment is a determination made by a court without a full trial. Such a judgment may be issued as to the merits of an entire case, or of specific issues in that case....

 in favor of Bushmaster Firearms, dismissing all of Colt's claims except for false advertising. On the latter claim, Colt could not recover monetary damages. The court also ruled that "M4" was now a generic name, and that Colt's trademark should be revoked.

Users

Used only by Afghan Army commandos
ANA Commando Battalion
The ANA Commando Brigade are part of the Afghan National Army and were formed from existing Infantry battalions. The program was established in early 2007 with the intent of taking one conventional battalion from each of the ANA corps, giving them special training and equipment and reorganizing...

. M4s sold as part of a 2006 Foreign Military Sales
Foreign Military Sales
The U.S. Department of Defense's Foreign Military Sales program facilitates sales of U.S. arms, defense equipment, defense services, and military training to foreign governments...

 package. Additional M4s sold as a 2008 Foreign Military Sales package.: Used by the Special Operations Command
Special Operations Command (Australia)
The Special Operations Command is a command within the Australian Defence Force . Special Operations Command was established in May 2003, to unite all of the ADF special forces units. As of 2007 Special Operations Command is fully operational. Australia's Special Operations Command is of...

, Clearance Divers
Clearance Diving Team (RAN)
The Clearance Diving Teams of the Royal Australian Navy also act as commando frogmen: they consist of naval personnel who are qualified in diving, demolitions, underwater repairs, and reconnaissance...

. and Police Tactical Group
Police Tactical Group
Police tactical groups , formerly known as "police assault groups", are part of the Australian government's National Anti-Terrorism Plan which, since 1978, has required each state and territory police force to maintain a specialised counter-terrorist and hostage rescue unit jointly funded by the...

s: Used by Bangladesh Paracommandos, Dhaka Metropolitan Police SWAT teams
SWAT (Bangladesh)
SWAT is an elite tactical unit of the Dhaka Metropolitan Police, Bangladesh. They operate under the Detective Branch of DMP. Eventually, the newly formed DMP unit SWAT is going to be expanded outwards forming one or more battalions...

 and Special Warfare Diving And Salvage
Special Warfare Diving and Salvage
The Special Warfare Diving and Salvage or SWADS is an elite Special Operations Force of the Bangladesh Navy.-Organization:The Bangladesh Special Warfare Diving and Salvage is a specially organized and elite team of highly trained personnel who are equipped and trained using many of the same...

: M4A1s sold as a 2008 Foreign Military Sales package.: M4s/M4A1s sold as part of a 2006 Foreign Military Sales package.: Used by Military Police of Rio de Janeiro State
Military Police of Rio de Janeiro State
The Military Police of Rio de Janeiro State like other military polices in Brazil is a reserve and ancillary force of the Brazilian Army, and part of the System of Public Security and Brazilian Social Protection...

.: C8 rifle.: The M4 Karabin A3 is used in small numbers by specialized units of the Czech Army
Military of the Czech Republic
The Army of the Czech Republic comprise the land forces, the Czech Air Force and support units. From the late 1940s to 1989, the extensive Czechoslovak Armed Forces formed one of the pillars of the Warsaw Pact military alliance...

. Known to be in use by the 601st Special Forces Group
601st Special Forces Group
The 601st Special Forces Group of general Moravec is a special forces unit of the Czech Armed Forces. It was officially created in 2003, the product of reorganizations in the Military of the Czech Republic in this year...

 in 2006 to replace the Sa vz.58.: M4A1s as part of a 2008 Foreign Military Sales.: M4s sold as a 2008 Foreign Military Sales package.: M4s sold as part of a 2007 Foreign Military Sales package. Additional M4s sold as a 2008 Foreign Military Sales package.: Georgian Armed Forces.: Used by EKAM
Special Anti-Terrorist Unit
The Special Suppressive Anti-Terrorist Unit is the Greek counter-terrorism unit of the Hellenic Police. It is the most distinguished part of the Hellenic Police...

.: M4A1 by Special Duties Unit
Special Duties Unit
The Special Duties Unit is an elite paramilitary tactical unit of the Hong Kong Police Force. Established in July 1974, it is a sub-division of the Police Tactical Unit...

 of the Hong Kong Police Force
Hong Kong Police Force
The Hong Kong Police Force is the largest disciplined service under the Security Bureau of Hong Kong. It is the world's second, and Asia's first, police agency to operate with a modern policing system. It was formed on 1 May 1844, with a strength of 32 officers...

: M4A1 SOPMOD by Hungarian Special Force : M4A1s as part of a 2008 Foreign Military Sales. M4A1 is also used by the Mizoram Armed Police
Mizoram Armed Police
Mizoram Armed Police is a Special Unit in the Police Department of Ministry of Home in the State of Mizoram, India. At present it comprises 3 Battalions with an additional 3 Indian Reserve Battalions...

, and Force One
Force One
The Force One is an elite commando force, which is a specialised counter terrorism unit to guard the Mumbai metropolitan area, one of the largest metropolitan areas in the world, formed by Government of Maharashtra on the lines of National Security Guards...

 of the Mumbai Police
Mumbai Police
The Mumbai Police is the police force of the city of Mumbai, India. It has the primary responsibilities of law enforcement and investigation within the limits of Mumbai. The department's motto is ""...

.: Used by Detachment 88 Counter-terrorism Police Squad operators. Also used by Komando Pasukan Katak
KOPASKA
Kopaska or Komando Pasukan Katak is the premier frogman and underwater demolition unit of the Indonesian Navy. The Unit's motto is 'Tan Hana Wighna Tan Sirna', which means 'There is no obstacle that can not be defeated'. It was officially established on March 31, 1962 by President Sukarno to help...

(Kopaska) tactical diver group and Komando Pasukan Khusus
Kopassus
Kopassus is an Indonesian Army special forces group that conducts special operations missions for the Indonesian government, such as direct action, unconventional warfare, sabotage, counter-insurgency, counter-terrorism, and intelligence gathering.Kopassus was founded on April 16, 1952...

(Kopassus) special forces group.: Used by the 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....

. Main weapon of the Iraqi National Counter-Terrorism Force.: Sold as part of a January 2001 Foreign Military Sales package to Israel.: Only Special Forces: M4s sold as part of a 2007 Foreign Military Sales package.: M4A1s as part of a 2008 Foreign Military Sales package. M4A1 SOPMOD rifles are in use by the Japanese Special Forces Group.: M4s sold as part of a 2007 Foreign Military Sales package. Additionals M4s sold as a 2008 Foreign Military Sales package.: M4 components being sold to Lebanese special forces
Lebanese Special Operations Command
The Lebanese Special Operations Command is the joint Special Operations command of the Lebanese Army which groups Lebanon's elite units. The command is part of the Lebanese Army Command.-Background:...

. M4/M4A1s sold as a 2008 Foreign Military Sales package.: M4s sold as a 2008 Foreign Military Sales package.: Made under license by SME Ordnance
SME Ordnance
The SME Ordnance Sdn Bhd company , formerly known as Syarikat Malaysia Explosive Sdn Bhd, is a Malaysian defense company that specializes in the manufacturing and marketing of ordnance...

 Sdn Bhd. To be used by the Malaysian Armed Forces, special forces of Malaysian Maritime Enforcement Agency
Malaysian Maritime Enforcement Agency
The Malaysian Maritime Enforcement Agency , the Malaysian Coast Guard version, is the principal government agency tasked with maintaining law and order and coordinating search and rescue operations in the Malaysian Maritime Zone and on the high seas. It is in effect the Coast Guard of Malaysia...

 and Royal Malaysian Police
Royal Malaysian Police
The Royal Malaysia Police is a part of the security forces structure in Malaysia. The force is a centralised organization with responsibilities ranging from traffic control to intelligence gathering. Its headquarters is located at Bukit Aman, Kuala Lumpur. The police force is led by an...

.: Sold as part of a 2005 Foreign Military Sales package.: Used by NZSAS operators and the police Armed Offenders Squad
Armed Offenders Squad
The Armed Offenders Squad is a specialist unit of the New Zealand Police designed to "cordon, contain and appeal to" armed and dangerous offenders. As the name explains, they are called upon when conflict with an armed offender has occurred or is considered imminent.The AOS draw upon a varied...

.: M4A1s sold as a 2008 Foreign Military Sales package.: M4/M4A1s sold as a 2008 Foreign Military Sales package. Two variants of the M4 carbine are made by Floro International Corporation
Floro International Corporation
Floro International Corporation is a Philippine company that produces a wide range of products for both the Philippine and export market.The company provides document conversion services and is ISO 9001 certified in the field of microfilming, digitizing, and indexing.They have gained some renown...

, consisting of the M4A1 5.56MM RIFLE and the M4A1 Model-C 5.56MM RIFLE.: Used by Polish special forces unit Grupa Reagowania Operacyjno-Manewrowego
GROM
GROM is one of five special forces units of the Polish Armed Forces. It was officially activated on July 8, 1990...

 (GROM).: Used by Marines special forces DAE (Destacamento de Acções Especiais).: Used by various police units.: Used by the Singapore Armed Forces Commando Formation
Singapore Armed Forces Commando Formation
The Singapore Armed Forces Commando Formation is an elite branch of the Singapore Armed Forces . An offensive unit, it specialises in pre-emptive operations involving small groups of specially trained soldiers in enemy territory...

.: Used by National Police Agency (Republic of China)
National Police Agency (Republic of China)
The National Police Agency is an agency under the Ministry of the Interior, Republic of China , which oversees all ROC police forces on a national level...

 : M4A1s sold as part of a 2006 Foreign Military Sales package.: M4/M4A1s sold as a 2008 Foreign Military Sales package.:Used by Special Forces
Special forces
Special forces, or special operations forces are terms used to describe elite military tactical teams trained to perform high-risk dangerous missions that conventional units cannot perform...

: Purchased 2,500 M4 carbines in 1993.: M4s sold as part of a 2006 Foreign Military Sales package.


U.S. citizen ownership

Sales of select-fire or full automatic M4s by Colt are restricted to military and law enforcement agencies. Only under special circumstances can a private citizen own an M4 in a select-fire or fully automatic configuration. While many machine guns can be legally owned with a proper tax stamp from the Bureau of Alcohol, Tobacco, Firearms and Explosives
Bureau of Alcohol, Tobacco, Firearms and Explosives
The Bureau of Alcohol, Tobacco, Firearms and Explosives is a federal law enforcement organization within the United States Department of Justice...

, an amendment to the Firearm Owners Protection Act
Firearm Owners Protection Act
The Firearm Owners' Protection Act , , codified at et seq., is a United States federal law that revised many statutes in the Gun Control Act of 1968.-Federal Firearms License regulatory reform:...

of 1986 barred the transfer to private citizens of machine guns made or registered in the U.S. after May 19, 1986. The only exception was for Special Occupational Taxpayers (SOT): licensed machine gun dealers with demonstration letters, manufacturers, and those dealing in exports and imports. As such, only the earliest Colt M4 prototypes built prior to May 19, 1986 would be legal to own by civilians not in the categories mentioned. However, US firearms law considers the lower receiver of a M16/M4 type rifle to be the "firearm" (the serial numbered and, in the case of machine guns, registered under federal law, part of the weapon). Therefore the more common registered Colt M16 may be configured as an M4 by replacing the M16 upper receiver/barrel assembly with an M4 upper half, and replacing the fixed rifle stock with a 4 or 6 position telescoping M4 stock.

External links

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