The HK 21/23 machineguns family emerged from original HK 21 machinegun, that is no longer manufactured by Heckler und Koch.
The HK 21 is a belt-fed general purpose machine gun using the 7.62 x 51 mm NATO cartridge. The method of operation of the HK 21 is the same as that used in the G3 rifle), employing a two-part breech block and delay rollers. The delayed blowback system, with a fluted chamber for easy cartridge movement, operates from the closed bolt position with a round in the chamber when the gun is ready to fire. Ammunition for HK 21 usually is carried in the disintegrating link belt and the gun will function using either the German DM 60 belt, the US M13 belt or the French belt. However, the continuous link belt DM 1, can also be used if required. Furthermore, by changing the barrel, the belt feed plate and the bolt, the gun can be converted to firing the 5.56 x 45 mm or the 7.62 x 39 mm cartridge. The utility of the weapon is further increased by inserting a magazine adaptor in place of the feed mechanism. This takes any of the Heckler and Koch 7.62 mm magazines intended for the G3 rifle or the HK 11 light machine gun. If required, the belt feed unit can be withdrawn and replaced with a magazine unit which fits into the receiver and is held by two locking pins. The unit allows the use of the 20-round box magazine or the 80-round double-drum plastic magazine. The gun may be fired at single shot or full automatic. The selector lever is above the pistol-grip and the trigger mechanism, disconnector and automatic sear are the same as those used in the G3 rifle.
HK 21 may be used from the integral bipods (as a light MG) or from the tripod mount.
The HK 21A1 is a development of the HK 21 (see previous entry) and the principal change is the omission of the option of using a magazine feed; the HK 21A1 is belt-fed only. The HK 21A1 uses the under-fed mechanism of its predecessor, but the mechanism can be hinged down to allow the belt to be inserted, making the operation of loading much quicker and easier.
Both HK 21 and HK 21A1 are currently discontinued by Heckler und Koch, but are still manufactured under licence in Portugal and Greece.
Currently, HK manufactures two models of improved original design: HK 21e in 7.62mm NATO and HK 23e in 5.56mm NATO (.223Rem). HK 23e is similar to HK 21E in every respect excluding the chambering and barrel lenght. The most major updates over the 21A1 are: slightly lenghtened receiver; fire control block wth semi-auto, 3-round bursts and full-auto modes of fire; Special bolt closing device for quiet bolt closure; re-design of the belt-feeding mechanism: the belt feed mechanism smoothly feeds the belted ammunition in two stages, during the reward and the forward movement of the bolt. The ability to use G3 or STANAG (for HK 23e) box or drum magazines is available with optional feed module kit (see picture) that consist of the bolt, recoil spring and belt feed module or magaine veil. The HK 21e has rear drum sight graduated up to 1200 meters and up to 1000 meters for HK 23e; both sights are ajustable for windage.
HK 21 is in service in Portugal and some African and Southeast Asian countries. HK 21A is in service with Greece. HK 21e is in service in Mexica and other countries. HK 21e and HK 23e are currently manufactured by HK in Germany for export.
HECKLER & KOCH GmbH P.O. Box 1329 D-78722 Oberndorf, Germany
Recoil operated, symetric roller-locked bolt system, firing from the closed bolt position
7,62mm NATO (HK21E) 5.56mm NATO (HK23E)
HK21E 9.3 kg on bipod; HK23E 8.7 kg on bipod
HK21E 1140 mm; HK23E 1130 mm
HK21E 550 mm; HK23E 450 mm
4 grooves, rh
box magazine 20 or 30 rounds or drum 80 rounds
belt 50 or 100 rounds
Rate of fire:
Serial number on rib of receiver top.
A combined safety catch and fire selector is on the left side of the receiver, above the pistol grip. UP for safe, midway for single shots (marked `E`) and fully DOWN for automatic fire (marked `A`)