page_title: Heckler & Koch HK21
section_title: Features
hierarchical_section_title: Heckler & Koch HK21 / Design details / Features
caption_attribution_description: English: The Heckler &amp; Koch HK21 Machine Gun
context_page_description: The HK21 is a German 7.62 mm 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 Asian, African and Latin American countries. It was also license-manufactured by Fábrica de Braço de Prata in Portugal as the m/968 and in Mexico by SEDENA as the MG21. In the German military and the federal police it is designated "G8".
context_section_description: 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 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 for a general-purpose machine gun rare closed bolt position. Firing from a closed bolt contributes to accurate fire, but is disadvantageous for heat dissipation. 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 HK21 has a  free-floating, heavy, quick-change barrel fitted with a slotted flash suppressor. The firearm is equipped with an iron sight line that consist of a rotary rear drum and hooded front post. The rear aperture sight is mechanically adjustable for both windage and elevation from 100–1,200 metres (109–1,312 yd) in 100 metres (109 yd) increments for 7.62×51mm NATO models or 100–1,000 metres (109–1,094 yd) in 100 metres (109 yd) increments for 5.56×45mm NATO models.
  By simply swapping out several components such as the barrel, bolt and feed plate unit, the weapon can be quickly converted to the intermediate 7.62×39mm and 5.56×45mm NATO chamberings.
caption: HK21 with ammunition belts and bipod positioned at the rear near its point of balance
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