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. Post front and two-leaf peep rear sights, with an A1 flash hider on the "C MP CHROME BORE" marked barrel, early pattern 1:12 twist rate, triangular handguard, checkered pistol grip and fixed buttstock. The upper receiver has the A1 pattern low profile casing deflector and an oval shaped forward assist, and the lower has a fenced magazine catch and right handed "SAFE"/"SEMI"/"AUTO" selector. A "C" marked full auto bolt carrier is installed, with an "MPC" marked bolt head, both matte black finished. With a black nylon sling.