This M4 Profile Crowned Barreled Upper Assembly is complete and ready for the addition of your sights or optic. The highly accurate 4150 Chrome Moly Vanadium steel barrel is chrome lined and rifled 1 x 9″ Right Hand twist. The muzzle is finished with a plain crown to comply with legal restrictions in States where threaded muzzles and flash hiders are prohibited. A MIL-STD-1913 Railed Gas Block is fitted – the bayonet lug has been machined off. The aluminum flat top Upper Receiver is complete with Bolt Carrier Assembly, Charging Handle, Forward Assist, Ejection Port Cover.