When Heckler & Koch produced the iconic G3 rifle, it was intended to be a parts of a complete small arms package. The G3 was the infantry rifle, and it was paired with the MP% submachine gun and the HK21 light machine gun for a complete set of weapons with the same manual of arms and disassembly/maintenance procedures. The first client for H&K was the West German Bundeswehr, and they were not interested in the HK21 - they had the MG3 already and were quite happy with it. Instead, Portugal would be the most significant early buyer of the HK21.

Mechanically, the HK21 shares all the same general principles of the G3. However, it has elements strengthened or modified to suit an LMG. These include a reinforced receiver, heavier recoil buffer, better long-range sights, and of course a quick-change barrel and a belt feed action. While an insert was made to allow use of G3 magazines in the original HK21, this was not a common practice. The receiver did not have the modular features that would come later on iterations like the HK21E; this was a gun really intended just for belt-fed use in 7.62x51mm NATO.

The HK21 was introduced in 1961, and Portugal adopted it as the m/968. Portugal actually purchased a license to produce the gun, and this particular example was one of many made at FMP in Portugal. The gun weighs 17.5 pounds (7.9 kg) and fires at 800-850 rpm. It is a relatively difficult gun to use well, with a comparatively harsh recoil for guns of its type. It did compete in the US LMG trials, but lost out to the FN Minimi.

Special thanks to Bear Arms in Scottsdale, AZ for providing access to this rifle for video!