This YHM barrel features a 5.56x45mm NATO chamber for full compatibility with surplus mil-spec ammunition or commercial 223 Remington ammunition. Constructed of 4140 chrome moly steel with a threaded muzzle, the barrel is Melonited for ultimate surface protection. The melonite coating provides a thinner surface than chrome-lining, so bore friction is reduced for better accuracy. In addition, melonite is harder than chrome-lining providing a longer wear life. This barrel is an excellent choice for a general-purpose AR rifle build. It is perfectly suited for use at the range, in a 3-Gun match, or in the field pursuing game. YHM-48-TF Surface: Diamond Fluted Length: 16.5 Mfg: Yankee Hill Machine Co., Inc.