Barrel: A proprietary blend of Hammer forged chrome molly vanadium made by FN that is referred to as "Machine Gun Steel" by virtue of its required use in FN's M249 and M240 weapons. The hammer forging process work hardens the steel, making it more durable. In addition, the chrome process for the bore allows for a lining almost twice as thick as a standard M16 for enhanced durability. Chambered in 5.56 NATO, with a 1:7 twist, M4 barrel extension, and a mid-length gas system. This heavy profile barrel is Mil-spec phosphate coated, High Pressure tested and Magnetic Particle inspected.