Introduced in 1967, the M16A1 (aka the Model 603) would be the standard issue rifle for the United States Army and Marine Corps until the 1980s. Developed from end-user feedback on the M16, the M16A1 introduced the "fenced" magazine catch to reduce the risk of accidentally ejecting the magazine during handling or movement, the forward assist upper receiver and bolt to help close a bolt that is obstructed by fouling or residue, and other minor adjustments. This example has been fitted with an A4 pattern upper marked "COLT 7.62x39" on the left side, with a JP tank-style muzzle brake on the "C MP 7.62X39 1/12 HBAR" barrel, KAC pattern quad rail forearm with Knight's brand vertical grip and cover panels, a detachable carry handle assembly, ARMS-M16 A1A2 rail, and an Aimpoint CompM dot sight. The lower receiver has the standard markings, with "SAFE", "SEMI", and "AUTO" positions for the right handed selector switch, checkered pistol grip, and a fixed buttstock. The bolt carrier is in proper full auto condition, with a matte gray head marked "7.62" with electric pencil.