HK21
Encyclopedia
The HK21 is a German
7.62mm general-purpose machine gun, developed in 1961 by small arms manufacturer Heckler & Koch
and based on the G3
battle rifle
. The weapon is in use with the armed forces of several Asia
n, Africa
n and Latin America
n countries. It was also license-manufactured by Fábrica do Braço de Prata
in Portugal
as the m/968 and in Mexico
by SEDENA as the MG21. In the German military (Bundeswehr
) and the federal police (Bundespolizei) it is designated "G8".
roller-delayed blowback-operated firearm with a semi-rigid locking mechanism designed to retard the rearward movement of the bolt. This delay was achieved by artificially increasing the inertia
of the bolt
by using an angular, interposed transmission system, installed symmetrically to the bore axis, with two cylindrical rollers acting as transmission elements against a movable locking piece which drives the heavy bolt carrier. The two-piece bolt assembly consists of a bolt head, which contains the aforementioned rollers, and a supporting locking piece and bolt carrier. During the "unlocking" sequence, the bolt head receives the recoil
impulse from the ignited cartridge and exerts rearward pressure against the rollers, seated in recesses in the barrel extension. The rollers are driven inward against angled ramps of the barrel extension and interact with the wedge-shaped locking piece, projecting it backwards. Thus a 4:1 transmission ratio is maintained (as long as the rollers move on the inclined surfaces of the barrel extension and locking piece) of the bolt carrier and locking piece relative to the bolt head; the bolt carrier travels backwards four times faster than the bolt head, ensuring a safe drop of pressure within the barrel prior to extraction. Since extraction is carried-out under relatively high pressure, the barrel’s chamber received a series of flutes designed to help free the bloated cartridge casing from the chamber walls.
The bolt features a spring-powered extractor
and an anti-bounce device that prevents the bolt head from glancing off the barrel extension upon forward return of the locking assembly. The lever-type ejector system is contained in the trigger group housing and is actuated with every shot by the recoiling bolt. The weapon has a hammer striker and is fired from the closed bolt
position. The trigger group, which is integrated with the pistol grip
and hinged from the receiver, is equipped with a fire control selector switch (selector lever in the "E" or "1" position – semi-automatic fire, "F" or "20" – continuous fire mode) that doubles as a manual safety (rotating the lever into the "S" or "0" setting disables the trigger, weapon is considered "safe").
The machine gun feeds from the left-hand side through a variety of disintegrating ammunition belt
types: the American
M13
linked belt, the German DM6 counterpart to the M13 or the segmented German DM1 belt. The ratcheting wheel feed unit was designed as an easily removable module that is inserted into the bottom portion of the feed block (installed in place of the standard magazine well), below the barrel axis. As a result of this configuration (the bolt passes over the belt), the ammunition belt is aligned upside down compared to most other belt-fed weapons (that is, the links face downward). The feed mechanism is actuated by the reciprocating movement of the bolt; a curved cam slot on the bottom of the bolt engages an actuator in the feed mechanism, rotating the double sprockets and positioning a new round in the feed path. Simple conversion from belt to magazine feed is possible by installing an adapter in the feed block which enables the use of H&K’s proprietary 20-round box magazine (from the G3 rifle) or a 50-round drum magazine
. The HK21 uses a modified G3 receiver that has been extended to the front sight base and is equipped with a detachable bipod
(mounted either in front of the feed mechanism or at the muzzle) and tripod and vehicle mounting points. The HK21 has close to a 48% parts interchangeability with the G3.
The HK21 has a heavy, quick-change barrel fitted with a slotted flash suppressor
and adjustable iron sight
s with a hooded foresight and an aperture rear sight adjustable from 100 through 1200 m in 100 m increments. By simply swapping out several components such as the barrel, bolt and feed unit, the weapon can be quickly converted to the intermediate 7.62x39mm and 5.56x45mm
calibers.
, German Navy
and the Federal Police use a variant of the HK11 designated the Gewehr-8 (or G8). It is tapped for telescopic sights and has a quick-change barrel with a bipod that uses either a heavy match-grade bull-barrel or a heavy barrel for automatic fire. It was designed to use G3-type 10- or 20-round box magazines in the designated marksman role, but could also use a special 50-round drum magazine for sustained supporting or suppressing fire. The modified G8A1 adopted the improvements of the HK11A1 series and was only able to feed from magazines and drums.
and several African and Asian armies. Both weapons, as in the original HK21, can be converted to chamber the 5.56x45 mm NATO round by replacing the appropriate components.
The "E" simply stands for "Export" model.
Compared to the older HK21A1 and HK11A1, the modernized "Export" weapons feature a longer barrel shroud, extended by 94 mm (3.7 in) towards the front, which also resulted in a longer sight radius; the barrel trunnion
was modified (the HK21E also received a longer barrel); a burst fire mode was incorporated into the trigger group as the fourth selector setting (3-round burst); a polymer barrel handle was added; the rear sight was modified with an adjustable drum; a bipod with a 3-position height adjustment mechanism replaced the simple folding bipod; the feed mechanism was modified to provide continuous feeding (by moving the belt in two stages, during both forward and rear movement of the bolt), a forward assist
for silent loading was provided and the machine guns were adapted to use NATO-standard optical sight mounts. When employed in the infantry assault role, the HK21E stores its ammunition belt in a 100-round sheet metal container, fastened to the bottom of the feed mechanism (as in the HK21A1). The ability to use G3
or STANAG
(for HK23E) box or drum magazines is available with an optional feed module kit that consists of the bolt, recoil spring and belt feed module or magazine well. The shock-absorbing tripod weighs 10.5 kg (23.1 lb).
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
7.62mm general-purpose machine gun, developed in 1961 by small arms manufacturer 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 based on the G3
Heckler & Koch G3
The G3 is a 7.62mm battle rifle developed in the 1950s by the German armament manufacturer Heckler & Koch GmbH in collaboration with the Spanish state-owned design and development agency CETME ....
battle rifle
Battle rifle
A battle rifle is a military service rifle that fires a full power rifle cartridge, such as 7.62x51mm NATO. While the designation of battle rifle is usually given to post-World War II select fire infantry rifles such as the H&K G3, the FN FAL or the M14, this term can also apply to older military...
. The weapon is in use with the armed forces of several Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n, Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
n and Latin America
Latin America
Latin America is a region of the Americas where Romance languages – particularly Spanish and Portuguese, and variably French – are primarily spoken. Latin America has an area of approximately 21,069,500 km² , almost 3.9% of the Earth's surface or 14.1% of its land surface area...
n countries. It was also license-manufactured by Fábrica do Braço de Prata
INDEP
INDEP - Indústrias Nacionais de Defesa, EP , originally Fábrica do Braço de Prata , is a defense industry company owned by the Portuguese Government...
in Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
as the m/968 and in Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
by SEDENA as the MG21. In the German military (Bundeswehr
Bundeswehr
The Bundeswehr consists of the unified armed forces of Germany and their civil administration and procurement authorities...
) and the federal police (Bundespolizei) it is designated "G8".
Design details
The HK21 is a selective fireSelective 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...
roller-delayed blowback-operated firearm with a semi-rigid locking mechanism designed to retard the rearward movement of the bolt. This delay was achieved by artificially increasing the inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
of the bolt
Bolt (firearm)
A bolt is a mechanical part of a firearm that blocks the rear of the chamber while the propellant burns.In manually-operated firearms, such as bolt-action, lever-action, and pump-action rifles and shotguns, the bolt is held fixed by its locking lugs during firing, forcing all the expanding gas...
by using an angular, interposed transmission system, installed symmetrically to the bore axis, with two cylindrical rollers acting as transmission elements against a movable locking piece which drives the heavy bolt carrier. The two-piece bolt assembly consists of a bolt head, which contains the aforementioned rollers, and a supporting locking piece and bolt carrier. During the "unlocking" sequence, the bolt head receives the 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...
impulse from the ignited cartridge and exerts rearward pressure against the rollers, seated in recesses in the barrel extension. The rollers are driven inward against angled ramps of the barrel extension and interact with the wedge-shaped locking piece, projecting it backwards. Thus a 4:1 transmission ratio is maintained (as long as the rollers move on the inclined surfaces of the barrel extension and locking piece) of the bolt carrier and locking piece relative to the bolt head; the bolt carrier travels backwards four times faster than the bolt head, ensuring a safe drop of pressure within the barrel prior to extraction. Since extraction is carried-out under relatively high pressure, the barrel’s chamber received a series of flutes designed to help free the bloated cartridge casing from the chamber walls.
The bolt features a spring-powered extractor
Extractor (firearms)
An extractor is a part in a firearm that serves to remove brass cases of fired ammunition after the ammunition has been fired. When the gun's action cycles, the extractor lifts or removes the spent brass casing from the firing chamber.-Overview:...
and an anti-bounce device that prevents the bolt head from glancing off the barrel extension upon forward return of the locking assembly. The lever-type ejector system is contained in the trigger group housing and is actuated with every shot by the recoiling bolt. The weapon has a hammer striker and is fired from the closed bolt
Closed bolt
A semi or full-automatic firearm which is said to fire from a closed bolt is one where, when ready to fire, a round is in the chamber and the bolt and working parts are forward...
position. The trigger group, which is integrated with the pistol grip
Pistol grip
On a firearm or other tool, the pistol grip is that portion of the mechanism that is held by the hand and orients the hand in a forward, vertical orientation, similar to the position one would take with a conventional pistol such as the M1911....
and hinged from the receiver, is equipped with a fire control selector switch (selector lever in the "E" or "1" position – semi-automatic fire, "F" or "20" – continuous fire mode) that doubles as a manual safety (rotating the lever into the "S" or "0" setting disables the trigger, weapon is considered "safe").
The machine gun feeds from the left-hand side through a variety of disintegrating ammunition belt
Belt (firearm)
A belt or ammunition belt is a device used to retain and feed cartridges into a firearm. Belts and the associated feed systems are typically employed to feed machine guns or other automatic weapons...
types: the American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
M13
M13 link
The M13 link, formally Link, M13, is the U.S. military designation for a disintegrating metallic link specifically designed for belt-fed firearms and rounds; it was introduced in the mid-20th century. It is the primary link type for the U.S., and among NATO for 7.62 mm ammunition...
linked belt, the German DM6 counterpart to the M13 or the segmented German DM1 belt. The ratcheting wheel feed unit was designed as an easily removable module that is inserted into the bottom portion of the feed block (installed in place of the standard magazine well), below the barrel axis. As a result of this configuration (the bolt passes over the belt), the ammunition belt is aligned upside down compared to most other belt-fed weapons (that is, the links face downward). The feed mechanism is actuated by the reciprocating movement of the bolt; a curved cam slot on the bottom of the bolt engages an actuator in the feed mechanism, rotating the double sprockets and positioning a new round in the feed path. Simple conversion from belt to magazine feed is possible by installing an adapter in the feed block which enables the use of H&K’s proprietary 20-round box magazine (from the G3 rifle) or a 50-round drum magazine
Drum magazine
A drum magazine is a type of firearms magazine that is cylindrical in shape, similar to a drum. Instead of rounds being stored flat, as in a more common box magazine, rounds in a drum magazine are stored in a spiral around the center of the magazine, facing the direction of the barrel.There are...
. The HK21 uses a modified G3 receiver that has been extended to the front sight base and is equipped with a detachable 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:...
(mounted either in front of the feed mechanism or at the muzzle) and tripod and vehicle mounting points. The HK21 has close to a 48% parts interchangeability with the G3.
The HK21 has a heavy, quick-change barrel fitted with a slotted flash suppressor
Flash suppressor
A flash suppressor, also known as a flash guard, flash eliminator, flash hider, or flash cone, is a device attached to the muzzle of a rifle or other gun that reduces the visible signature of the burning gases that exit the muzzle. This reduces the chances that the shooter will be blinded in dark...
and adjustable iron sight
Iron sight
Iron sights are a system of shaped alignment markers used as a sighting device to assist in the aiming of a device such as a firearm, crossbow, or telescope, and exclude the use of optics as in telescopic sights or reflector sights...
s with a hooded foresight and an aperture rear sight adjustable from 100 through 1200 m in 100 m increments. By simply swapping out several components such as the barrel, bolt and feed unit, the weapon can be quickly converted to the intermediate 7.62x39mm and 5.56x45mm
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...
calibers.
G8 and G8A1
The German ArmyGerman Army
The German Army is the land component of the armed forces of the Federal Republic of Germany. Following the disbanding of the Wehrmacht after World War II, it was re-established in 1955 as the Bundesheer, part of the newly formed West German Bundeswehr along with the Navy and the Air Force...
, German Navy
German Navy
The German Navy is the navy of Germany and is part of the unified Bundeswehr .The German Navy traces its roots back to the Imperial Fleet of the revolutionary era of 1848 – 52 and more directly to the Prussian Navy, which later evolved into the Northern German Federal Navy...
and the Federal Police use a variant of the HK11 designated the Gewehr-8 (or G8). It is tapped for telescopic sights and has a quick-change barrel with a bipod that uses either a heavy match-grade bull-barrel or a heavy barrel for automatic fire. It was designed to use G3-type 10- or 20-round box magazines in the designated marksman role, but could also use a special 50-round drum magazine for sustained supporting or suppressing fire. The modified G8A1 adopted the improvements of the HK11A1 series and was only able to feed from magazines and drums.
GR-series
The GR-series were "sanitized" (i.e., having no serial numbers or identifying marks) Heckler & Koch weapons used by special operations forces. They differed from the stock weapons in that they had optical sights, no provisions for iron sights, and came standard in Woodland (-C suffix) or Desert (-S suffix) camouflage.- GR-6 Automatic Rifle (HK13).
- GR-9 Light Machinegun (HK23).
HK21A1
In the early 1970s the HK21’s design was simplified and the feed mechanism was modified. The machine gun's weight was increased, a carrying handle and a hooked buttstock with improved buffer mechanism were also added. Since then, the HK21 was offered in two main variants: the HK21A1 general-purpose machine gun (with a different belt feed mechanism) and the HK11A1 automatic rifle (optimized for magazine feed only). The HK11A1 proved more successful in export sales and was adopted by the Hellenic ArmyHellenic 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...
and several African and Asian armies. Both weapons, as in the original HK21, can be converted to chamber the 5.56x45 mm NATO round by replacing the appropriate components.
HK21E
During the 1980s both the HK21A1 and HK11A1 were modernized, resulting in a new modular family of machine guns that share the same receiver, trigger group and interchangeable barrels and feed units, consisting of:- HK11E automatic rifle (magazine fed, chambered in 7.62x51 mm NATO caliber)
- HK13E automatic rifle (magazine fed, chambered in 5.56x45 mm NATO caliber)
- HK21E general-purpose machine gun (belt feed, 7.62x51 mm NATO), which is also license-built in Mexico for the armed forces
- HK23E light machine gun (belt-fed, 5.56x45 mm NATO).
The "E" simply stands for "Export" model.
Compared to the older HK21A1 and HK11A1, the modernized "Export" weapons feature a longer barrel shroud, extended by 94 mm (3.7 in) towards the front, which also resulted in a longer sight radius; the barrel trunnion
Trunnion
A trunnion is a cylindrical protrusion used as a mounting and/or pivoting point. In a cannon, the trunnions are two projections cast just forward of the centre of mass of the cannon and fixed to a two-wheeled movable gun carriage...
was modified (the HK21E also received a longer barrel); a burst fire mode was incorporated into the trigger group as the fourth selector setting (3-round burst); a polymer barrel handle was added; the rear sight was modified with an adjustable drum; a bipod with a 3-position height adjustment mechanism replaced the simple folding bipod; the feed mechanism was modified to provide continuous feeding (by moving the belt in two stages, during both forward and rear movement of the bolt), 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...
for silent loading was provided and the machine guns were adapted to use NATO-standard optical sight mounts. When employed in the infantry assault role, the HK21E stores its ammunition belt in a 100-round sheet metal container, fastened to the bottom of the feed mechanism (as in the HK21A1). The ability to use G3
Heckler & Koch G3
The G3 is a 7.62mm battle rifle developed in the 1950s by the German armament manufacturer Heckler & Koch GmbH in collaboration with the Spanish state-owned design and development agency CETME ....
or 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...
(for HK23E) box or drum magazines is available with an optional feed module kit that consists of the bolt, recoil spring and belt feed module or magazine well. The shock-absorbing tripod weighs 10.5 kg (23.1 lb).
HK25
A heavy machine gun variant of the HK21 chambered in 12.7x99mm NATO also existsUsers
- HK11A1 and HK21A1 variants.: HK21A1 variant.: HK21 variant.: HK21E1 variant. : HK11A1 variant. Made under license.: HK21E variant.: HK21A1 variant.: HK11A1 and HK21E variants.: HK21A1 variant.: HK11 and HK21 variants.: HK21 variant.: HK21 variant. Made under license.: HK21 variant.: HK21 variant.: HK11 and HK21 variants.: HK21 variant.: HK23E variant is employed by the Turkish GendarmerieTurkish GendarmerieThe Turkish Gendarmerie is a branch of the Turkish Armed Forces and it is responsible for the maintenance of the public order in areas that fall outside the jurisdiction of police forces , as well as assuring internal security and general border control along with carrying out other specific...
.: HK23E variant.: Used by Delta ForceDelta Force1st 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...
in Operation Eagle ClawOperation Eagle ClawOperation Eagle Claw was an American military operation ordered by President Jimmy Carter to attempt to put an end to the Iran hostage crisis by rescuing 52 Americans held captive at the U.S. Embassy in Tehran, Iran on 24 April 1980...
in 1980.