Heckler & Koch HK 21

General Purpose Machine Gun / Light Machine Gun / Automatic Rifle [ 1961 ]

Despite its 1960s origins, the HK21 general purpose machine gun is still in use around the globe today.

Authored By: JR Potts, AUS 173d AB and Dan Alex | Last Edited: 02/14/2022 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site.

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In 1949, Heckler & Koch GmbH was formed at Oberndorf am Neckar in West Germany to become a small arms weapons designer and manufacturer. Today, HK is one of the world's finest small arms producers whose product line has since included battle rifles, assault rifles, submachine guns, personal defense weapons, designated marksman rifles, sniper rifles and various air-cooled machine guns. HK saw an opportunity in 1961 to branch out and design a new "universal" machine gun and this development became the "HK21" series. The HK 21 was formally categorized a as "general purpose machine gun" (GPMG) - though it is also considered a "light machine gun" (LMG) - and went on to spawn of family of support weapon. The family was based on the hugely successful HK G3 Battle Rifle / Assault Rifle which went on to see widespread use around the world. The original G3 automatic rifle design utilized a 20-round straight detachable box magazine as well as a 50-round drum for supporting fire. Since the HK21 originated from the G3, the HK21 utilized a similar receiver, could operate from a ammunition magazine or belt feed and incorporated a detachable bipod for stabilization in the fire support role.

The HK21 was initially designed as a belt-fed weapon however an adapter was then produced to allow the use of box magazines or an ammunition drum. All Heckler & Koch machine guns (including the HK21) feature the same successful roller-delayed blowback action - based on the original late-World War 2-era StG45 prototype - with a fixed barrel. A two-part breech block and roller delays were standard and a smooth extraction was due to a fluted chamber. The firing action was sequenced by a two-position lever to facilitate either single, semi-automatic fire or for full-automatic fire. If the operator wanted to fire the 7.62x39mm or the 5.56x45mm standard cartridge a simple change of barrel, feed plate and the bolt would suffice in creating an all-new weapon platform. To prevent the bolt from striking obliquely against the barrel and return the lock assembly, a spring-powered extractor was used. The recoiling bolt utilized energy from the preceding shot and would extract the cartridge via this lever ejector system. The selector switch was labeled clearly with an "E" for semi-automatic fire, an "F" for full-automatic fire and rotating the lever to the "0" or "S" setting would block firing to enter a "safety" mode.

To accept a number of multiple ammunition feed systems HK also devised a module to allow use of the German DM6 and DM1 belt as well as the American M13 belt. This module was fitted below the weapon in which the bolt would pass over the ammunition belt - set upside down so the links face down. The new round was then fed into position by the reciprocating action of the bolt. A heavy barrel with a flash suppressor was standard as were adjustable iron sights, this consisting of a forward and rear sight with the rear sight ranging from 100m to 1200m in 100m increments. The HK21 was given a fixed, though adjustable and removable, polymer stock. A collapsible carrying handle located at the center mass of the weapon was provided for ease of transportation of the weapon in whole. In addition to a bipod, the HK 21 could be affixed to a tripod or vehicle pintle mount.

After some time in the field, the HK21 line was simplified and improved to become the HK21A1 in the 1970s. The HK11 series was similar to the HK21 though differentiated by its magazine-only feed and classification as an automatic rifle. The HK21E was an export model chambered for the 7.62x51mm NATO cartridge. The HK23E was an export light machine gun chambered for the 5.56x45mm NATO cartridge. The HK13E was another automatic rifle development and fed by magazines holding 5.56x45mm NATO cartridges. The HK G8 offered telescopic sights, a quick-change barrel and various box magazine and one drum magazine ammunition count. The HK GR-6 and GR-9 were issued to special forces units and had their serial identifiers removed. The GR-6 represented the automatic rifle form while the GR-9 was the light machine gun form.

Portugal license-produced the HK21 as the m/986 while Mexico designated their local variants (HK21E) as the MG21 with production by SEDENA.©MilitaryFactory.com

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Specifications

Heckler and Koch GmbH - Germany / SEDENA - Mexico / Fabrica do Braco de Prata - Portugal
Manufacturer(s)

Bangladesh; Brazil; Cameroon; Colombia; Chile; Croatia; Cyprus; Ecuador; El Salvador; West Germany; Germany; Greece; Jordan; Malaysia; Mexico; Niger; Nigeria; Portugal; Paraguay; Sri Lanka; Thailand; Turkey; United States
Operators

1961
Service Year

Germany
National Origin

AUTOMATIC FUNCTION
Features a mechanical function to automate the firing action.

FIRE SUPPORT
Capable of suppressing enemy elements at range through direct or in-direct fire.

1,020 mm
(40.16 inches)
Overall Length

450 mm
(17.72 inches)
Barrel Length

16.09 lb
(7.30 kg)
Empty Weight

Delayed Blowback; Selective Fire
Action

BLOWBACK OPERATION
Gas pressure from the rearward movement of the ignited cartridge case provides the needed bolt movement, ejecting the spent case and stripping a fresh case from the magazine.

7.62x51mm NATO; 5.56x45mm NATO
Caliber(s)
May not represent an exhuastive list; Calibers may be model-specific dependent; Always consult official manufacturer sources.

Metal Link Belt; 10- or 20-round box magazine; 50-round drum
Rounds

Hooded Front Post; Rear Rotary Diopter Drum
Sights

Material presented above is for historical and entertainment value and should not be construed as usable for hardware restoration, maintenance, or general operation - always consult official manufacturer sources for such information.

6,600 feet
(2,012 meters | 2,200 yards)
Max Effective Range

900
Rounds-per-Minute
Rate-of-Fire

2,700 ft/sec
(823 m/sec)
Muzzle Velocity

HK21 - Base General Purpose Machine Gun

HK21A1 - General Purpose Machine Gun; simplified production model; revised feed mechanism; increased weight; carrying handle; hooked-style buttstock; magazine and belt feed.

HK11A1 - Automatic Rifle; magazine feed only.

HK21E - Modernized HK 21; general purpose machine gun; belt fed; chambered for 7.62x51mm NATO round; export model.

HK11E - Modernized HK 11; automatic rifle; magazine fed; chambered for 7.62x51mm NATO round; export model.

HK23E - Light Machine Gun; belt-fed; chambered for 5.56x45mm NATO round; export model.

HK13E - Automatic Rifle; magazine fed; chambered for 5.56x45mm NATO round; export model.

HK G8 / Gewehr G8 - Telescopic sights; quick-change barrel; bipod; 10- or 20-round box magazines OR 50-round drum.

HK G8A1 / Gewehr G8A1 - Based on the HK 11A1 model; magazine and drum feeds.

HK GR-6 - Automatic rifle based on the HK 13; sans serial numbers and iron sights; optical sights; wood and desert camouflage patterns.

HK GR-9 - Light machine gun based on the HK 23; sans serial numbers and iron sights; optical sights; wood and desert camouflage patterns.

m/968 - Portuguese license-production HK 21 under Fabrica do Braco de Prata.

MG21 - Mexican license-production HK 21E under SEDENA.

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