Match-quality 18” 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 .308 Winchester, button rifled with 1-10 twist rifling, and machined to a standard medium weight exterior profile. Gas port drilled for a mid length gas system, .750″ diameter at the gas block. 5/8”-24 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).