Heckler & Koch HK 21

HK (or Heckler & Koch) is a small arms weapons designer and manufacturer owned by the British company, BAE Systems, though the company itself is located in Oberndorf Neckar, Germany. HK is one of the world’s finest small arms producers whose product line delves into assault rifles, submachine guns and various air-cooled machine guns. HK saw an opportunity in 1961 to branch out and design a new universal machine gun, with this design becoming the HK 21. The HK 21 fell into the general purpose light machine gun family and used the stellar G3 automatic rifle as a model. The G3 automatic rifle design used a 20-round box magazine or a 50-round drum. As the G3 was the blueprint for the HK 21, the HK 21 used a similar receiver along with a detachable bipod.

The HK 21 was designed to be belt-fed however an adapter was produced to allow the use of box magazines or an ammunition drum. All Heckler & Koch machine guns (including the HK 21) feature the same successful delayed blowback action with a stationary barrel. A two-part breech block and roller delays were standard with smooth extraction was due to a fluted chamber. The firing action was sequenced by a two-position lever to accept single rounds or allow for full automatic fire. If the operator wanted to fire the 7.62x39mm or the 5.56x45mm round a simple change of barrel, feed plate and the bolt would suffice. To prevent the bolt from striking obliquely against the barrel and return the locking assembly, a spring-powered extractor was used. The recoiling bolt utilized energy from a shot and would extract the cartridge via this lever ejector system. The selector switch was labeled 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 a "safe" mode.

To accept a number of multiple ammunition feed systems HK devised a module to allow use of the German DM6 and DM1 belt and the American M13 belt. The module was fitted below the weapon in which the bolt would pass over the ammo 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 iron adjustable 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 in the center mass was provided for easy carrying of the weapon. In addition to a bipod, the HK 21 could be affixed to a tripod or vehicle, the latter via a pintle mount.

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Last Updated: 4/22/2009