16" Barrel LengthChrome Moly Steel BarrelCarbine Length Gas SystemM4 Profile (uses .750 diameter gas block)5.56 NATO Chamber1 in 7" Barrel TwistNitride Barrel Finish Please check the barrel closely for any irregularities. It is the builder's responsibility to check headspace before assembling. In the unlikely event you have an obvious issue with a barrel, STOP AND DO NOT ASSEMBLE or modify. Contact Customer Service for warranty replacement. Barrel is non-returnable if it has been installed, fired or modified from original shipped state.