Quick view CMMG CMMG Barrel Sub-assembly, Cmmg 30df80a Barrel 16.1 Mr 4140cm 300 $202.24 $171.30 Cmmg's barrel sub-assembly is ideal for building your custom ar-15 upper group.It comes with properly installed m4 barrel extension.The barrel is constructed of 4140 chrome moly with a slat bath nitride finish and 5/8x24" threads.Caliber Or Gauge: 300... Compare Add to Cart