16" 416R Stainless steel barrel, chambered in 5.56 NATO with a 1:7 Twist with an M4 Barrel extension. Barrel is a mid-length gas, A2-style profile, with a .750" Gas block area. Please check the barrel closely for any irregularities. It is the builder's responsibility to check headspace before assembling. In the unlikely event you have an issue with a barrel, STOP AND DO NOT ASSEMBLE. Contact Customer Service.