Match-quality 16” barrel feature Nitromet salt bath nitride to give them maximum wear resistance and durability that standard barrel finishes just can’t match. Barrel has a Nitromet nitrided bore treatment for longer life than chrome without affecting accuracy. Barrels are made of 4150 CrMoV, chambered for 5.56mm NATO, button rifled with 1-7 twist rifling, and machined to a standard government exterior profile. Gas port drilled for a mid length gas system, .750″ diameter at the gas block. ½”-28 threads on the muzzle end. Comes with a NiB-X coated barrel extension installed to help the bolt unlock exceptionally smoothly, especially when used with a WMD NiB-X coated bolt and complete BCG (available separately).