DSArms offers the Z4 GTC with the Corrosion Resistant Operating System (C.R.O.S.) The rifle features a 16-inch M-4 profile fluted 1:9 twist chrome lined heavy barrel, 5.56 NATO, chrome lined picatinny gas block with removable, fixed front sight, and six position collapsible M-4 stock. C.R.O.S. eliminates the problematic features of the standard AR gas system such as gas rings, leaking gas tube, leaking gas key, carbon build up in the bolt, heat into the carrier assembly which causes extractor and extractor spring issues. The gas trap system also reduces recoil for smoother, more accurate operations.