Match-quality 18in barrel feature Nitromet salt bath nitride to give wear resistance and durability that standard barrel finishes can't match. The barrel has a Nitromet nitrided bore treatment for longer life than chrome without affecting accuracy. Barrels are made of 4150 Chrome Moly Vanadium (CrMoV), chambered for .308 Winchester, button rifled with 1-10 twist, and machined to a light or standard medium weight exterior profile. Gas port drilled for a mid length gas system, .750in diameter at the gas block. 5/8in-24 threads on the muzzle end. Comes with a NiB-X coated barrel extension installed to help the bolt unlock smoothly, especially when used with a WMD NiB-X coated bolt and complete BCG (sold separately).