5.56 NATO Chamber4150 CrMoV (Chrome Moly Vanadium per MIL-B-11595E)1/7 Twist Six Groove1/2-28 Threaded Muzzle.750? Gas Block Journal19 OuncesQPQ Corrosion Resistant FinishQPQ coated M4 Feed Ramp ExtensionHigh Pressure (proof) Tested (HPT)Magnetic Particle Inspected (MPI)