7.62 X 28 TYPE III XPL

Research notes

The U.S. Air Force Armament Technology Lab modified the 221 Multi-Purpose Weapon during 1973 with a .30 Cal barrel fitted with a silencer. Three different versions were tested of which this is the third version that is, like the second version, based on the 5,56 NATO case shortened to 1,10 inches, the first version being based on the 30 M1 Carbine case. The third version differs from the previous two in having a slight bottle neck, in all probability to fix headspace problems. See also HWS 3 p.419 Fig 616.