Perfect for building your custom Mk4 upper group. Comes with properly installed M4 barrel extension. All barrel sub-assemblies are properly headspaced. Made of 4140CM with a SBN Finish. – CALIBER: .350 Legend – BARREL: 16.1 1:16 twist medium taper 4140CM SBN – MUZZLE: Threaded 1/2-28 (9mm) – GAS PORT LOCATION: Carbine Length .750 Gas Block Journal – WEIGHT: 1lb 9oz