WMD Guns 5.56 NATO 16in Government Profile 1-7 Mid Length RH 4150 CrMoV Nitride Black. 56 Barrel has been treated with Nitromet (salt bath nitrocarburized) inside and out with a hardened finish that results in a bore life 40percent greater than with traditional chrome-lining without affecting accuracy. Barrels are made of 4150 Chrome Moly Vanadium steel chambered for 5.56mm NATO and machined to a standard profiles. Specifications for WMD Guns 5.56 NATO Nitromet Barrel: Manufacturer: WMD Guns Color: Black Finish: Nitride Caliber: 5.56x45mm NATO Gas Block Journal Size-Diameter: .750 in Threads per Inch: 1/2x28 Barrel Material: 4150 Chrome Moly Vanadium Gun Make: AR Platform Condition: New Gas System Type: Blowback Gun Type: Rifle Package Contents: WMD Guns 5.56 NATO Nitromet Barrel WMD Guns 556B16M1-7GP: 5.56 NATO 16in Government Profile1:7 Mid Length RH 4150 CrMoV Nitride Black