Colt CR6921 M4 Carbine 5.56 NATO, 14.5 inch barrel semi-automatic rifle. Chrome-lined 14.5-inch M4 contour barrel with A2 flash suppressor; Flat-top receiver and Magpul folding rear sight; Gas-operated action with 1:7 RH twist; Lightweight carbine with black anodized hardcoat finish on forged receivers and dual aluminum shielding in the handguard for heat protection.