Heckler & Koch HK21

Infobox Weapon
name=HK21


caption=
origin=flag|West Germany
type=General purpose machine gun
is_ranged=yes
service=
used_by=See "Users"
wars=
designer=Heckler & Koch
design_date=1961
manufacturer=Heckler & Koch
production_date=
number=
variants=See "Variants"
weight=kg to lb|7.92|sp=us|abbr=on|precision=2|wiki=yes (HK21) convert|8.30|kg|abbr=on (HK21A1) convert|7.70|kg|abbr=on (HK11A1) convert|9.30|kg|abbr=on (HK21E) convert|8.15|kg|abbr=on (HK11E) convert|8.75|kg|abbr=on (HK32E) convert|8.00|kg|abbr=on (HK13E)
length=mm to in|1021|abbr=on|precision=1|wiki=yes (HK21) convert|1030|mm|abbr=on|1 (HK21A1, HK11A1, HK11E, HK23E, HK13E) convert|1140|mm|abbr=on|1 (HK21E)
part_length=convert|450|mm|abbr=on|1 (HK21, HK21A1, HK11A1, HK11E, HK23E, HK13E) convert|560|mm|abbr=on|1 (HK21E)
crew=
cartridge=7.62x51mm NATO (HK21, HK21A1, HK11A1, HK21E, HK11E) 5.56x45mm NATO (HK23E, HK13E)
action=Roller-delayed blowback
rate=900 rounds/min (HK21, HK21A1) 800 rounds/min (HK11A1, HK21E, HK11E) 750 rounds/min (HK23E, HK13E)
velocity=convert|800|m/s|0|lk=on|sp=us|abbr=on (HK21, HK21A1, HK11A1, HK11E) convert|840|m/s|abbr=on|1 (HK21E) convert|910|m/s|abbr=on|1 (HK23E, HK13E using the SS109 cartridge)
range=100 to 1,200 m sight adjustments
max_range=
feed=M13, DM6, DM1 ammunition belt, 20-round detachable box magazine (from the G3) or 50-round drum
sights=Rear rotary diopter drum; hooded front post

The HK21 is a German 7.62 mm general purpose machine gun, developed in 1961 by arms manufacturer Heckler & Koch and based on the 7.62 mm G3 automatic rifle. It fires the 7.62x51mm NATO rifle cartridge. The weapon is in use with the armed forces of several Asian, African and Latin American 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.

Design details

The HK21 is a selective fire 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 since 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 ammunition belt is aligned upside down compared to most other belt-fed weapons (that is, the link ridges face downward). The feed mechanism is actuated by the reciprocating movement of the bolt. Simple conversion from belt to magazine feed is possible by installing an adapter in the feed block that enables the use of HK’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 two-point bipod adapter and tripod mounting points.

The HK21 has a heavy, quick-change barrel fitted with a flash suppressor and adjustable iron sights with a hooded foresight and 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.

Variants

In the early 1970s the HK21’s design was simplified, the feed mechanism was modified; the buttstock and carrying handle were also changed. 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 Army and several other African and Asian armies. Both weapons, as in the original HK21, can be converted to chamber the 5.56x45mm NATO round by replacing the appropriate components.

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: the 7.62 mm HK11E automatic rifle (magazine fed, chambered in 7.62x51mm NATO); the 5.56 mm HK13E light machine gun (magazine fed, 5.56x45 mm NATO caliber); the 7.62 mm HK21E general purpose machine gun (belt feed, 7.62x51mm NATO), which is also license-built in Mexico for the armed forces and the 5.56 mm HK23E light machine gun (belt-fed, 5.56x45mm NATO). The "E" in simply stands for "Export"

Compared to older HK21A1 and HK11A1, the modernized weapons feature a longer receiver, extended by convert|94|mm|abbr=on|1 towards the front, which also resulted in a longer sight radius; the barrel trunion 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 convert|10.5|kg|abbr=on.

Users

*flag|Bangladesh: HK11A1 and HK21A1.
*flag|Brazil: Rio de Janeiro's BOPE.
*flag|Cameroon
*flag|Colombia
*flag|Chile
*flag|Cyprus
*flag|Ecuador
*flag|Germany: A variant of the HK11E known as the G8 is used in small numbers by various specialized units and the German border police ("Bundespolizei"). There is a G8A1 variant which will not accept the belt feed mechanism and is restricted to use with magazines. The barrel is heavier than usual, precisely rifled, and capable of being changed rapidly when the weapon is being used in the automatic fire mode.
*flag|Greece: Adopted the HK11A1 as a standard light machine gun. Manufactured under license by Hellenic Arms Industry (now Hellenic Defense Systems). [ [http://www.eas.gr/index.php?lang=en&sec=7&cid=116 Hellenic Defense Systems ] ]
*flag|Malaysia: Uses both the HK11A1 and the HK21E.
*flag|Mexico
*flag|Niger: HK11A1 and HK21.
*flag|Nigeria
*flag|Portugal: Standard machine gun, designated m/968 and produced by Fábrica do Braço de Prata.
*flag|Paraguay
*flag|Sri Lanka
*flag|Thailand: Used by the Royal Thai Navy SEALs.
*flag|United States: The U.S. National Aeronautics and Space Administration utilizes the HK21E in providing security for the Kennedy Space Center.

ee also

*CETME Ameli
*FN Minimi

Notes

References

* Hogg,Ian & Weeks, John S. "Military Small Arms of the 20th Century:6th edition"DBI Books.ISBN 0-87349-120-3

External links

* [http://www.hkpro.com/hk21e.htm HKPRO]
* [http://world.guns.ru/machine/mg18-e.htm Modern Firearms]
* [http://remtek.com/arms/hk/mil/21/21.htm REMTEK (HK21E)]
* [http://remtek.com/arms/hk/mil/23/23.htm REMTEK (HK23E)]