Bushmaster M4 Upper Receiver Kit, ready to complete your build. Kit includes fully assembled A2 upper receiver, bolt carrier group, handguards and charging handle. Upper features a 11.5″ M4 barrel which is machined from 4140 chrome moly steel, chrome lined, has a 1-9 twist, has a front sight base installed on a .750″ barrel shoulder, 1/2-28 muzzle threads and an A2 flash hider installed. Upper receiver has M4 feed ramps, as well as an A2 rear sight. Included complete bolt carrier group has a matte black phosphate finish, is chrome lined and is magnetic particle inspected. All NFA rules apply. Mfg: Bushmaster Firearms Int.Llc.