HK-21 / HK-23

The HK21 was developed in 1961 by the West German manufacturer Heckler & Koch. The design is based on the G3 battle rifle and was produced as a general-purpose machine gun. Licensed production was established in Portugal by Fábrica de Braço de Prata as the m/968 and in Mexico by SEDENA as the MG21.

The firearm utilizes a selective fire, roller-delayed blowback operating system with a semi-rigid locking mechanism. This system employs two cylindrical rollers and a wedge-shaped locking piece to retard bolt movement, using a transmission ratio to ensure chamber pressure drops before extraction. To facilitate extraction, the chamber features internal fluting. The bolt assembly includes an anti-bounce mechanism with a spring-loaded locking lever to prevent rebounds off the barrel’s breech surface. The weapon fires from a closed bolt position and features a quick-change, free-floating barrel. The receiver is a modified G3 component extended to the front sight base, equipped with a pistol grip, a carrying handle, and a hooked buttstock. The feed system is positioned on the left side and utilizes a ratcheting wheel module that pulls ammunition belts through the bottom of the feed block, resulting in the belt links facing downward. The weapon can be converted between belt and magazine feeding through the installation of a feed block adapter.

The weapon entered service in 1961 and was adopted by military and internal security forces across Asia, Africa, and Latin America. In Germany, the federal police and military designated the HK11 variant as the G8. The United States Navy SEALs and Delta Force employed the weapon during and after the Vietnam War, including use in Operation Eagle Claw. Variants include the HK21A1, which introduced a modified feed mechanism and polygonal rifling, and the Export series. The HK21E and HK23E feature a lengthened receiver, internal reinforcing bars, and a four-position trigger group including a three-round burst setting. Specialized versions include the GR-series for special operations forces, which lack identifying marks, and the HK11 and HK13, configured for magazine feeding. The weapon has been deployed in various conflicts, including the Portuguese Colonial War, the South African Border War, and the Salvadoran Civil War.