With the standardization of the RIFLE, 5.56 MILLIMETER, M16A2 (NSN 1005-01-128-9936), on 30 March 1982, Colt Defense LLC (CAGE 13629) set about to produce a carbine version of the M16A2 as they did for the M16A1 rifle. In early 1985, Colt unveiled the " M16A2 Carbine ," which essentially was an improved version of the CARBINE, 5.56 MILLIMETER, M16A1 (NSN 1005-01-029-3866; also known as the model RO653 carbine). The weapon was marketed to both military and law enforcement as " ...smaller, more compact versions of the M16A2 Rifle, intended for use wherever lightness and speed of action is required. " The M16A2 carbine's "lightweight" 14.5-inch barrel was upgraded from the M16A1 carbine's 1:12 twist rate to a 1:7 twist rate. This was done to improve performance of the barrel with the NATO STANAG 4172 62 grain SS109 5.56 x 45mm cartridge. The SS109 cartridge would later be standardized, on 10 June 1983, by the United States government as the...