The HK21 is the civilian semi-automatic version of the HK21 general-purpose machine gun, sharing the G3 roller-delayed blowback mechanism in a belt-fed or magazine-fed configuration. In its civilian semi-automatic form, it is a rare collector piece that demonstrates the HK system's adaptability. Military versions served with German and Portuguese forces. Type: Semi-Auto Rifle Action: Roller-Delayed Blowback Caliber: 7.62x51mm NATO Capacity: 20 Year introduced: 1961, Germany Weight: 17.9 oz Overall length: 40.16" Status: Discontinued Military use: Yes Intended use: Collector, Military Use