LE6921 Carbine Upper Assembly chambered in 5.56x45 NATO complete with bolt carrier assembly and charging handle. - 14.5 Chrome Lined Barrel with 1-7 RH Twist Flat-top Receiver Flip-up Rear Sight Bayonet Lug and Screw on Flash Hider includes Pivot Pin Adapter to mount upper on Colt lower receivers with large pivot pins. The bolt carrier assembly that is included with this upper assembly is current production and may not work with some Colt rifles equipped with a steel sear block.