M4E1 Threaded Upper Receiver Features a new enhanced forging that gives the upper receiver a ""billet look"". The new picatinny profile that blends seamlessly with the Aero Enhanced R-Series Handguards. The receivers feature M4 Feedramps .250 takedown pin holes, Laser engraved T-marks, and includes port door and forward assist installed. The Brownells M16 5.56 Complete Bolt Carrier Group is constructed with a bolt made from 9310 steel, which is finished with a heat treatment and shot peening. The carrier is fabricated from 8620 hardened steel. Each element of the bolt-carrier group is finished in a black-nitride coating. The Brownells M16 5.56 Complete Bolt Carri Mfg: Brownells
