ANDERSON AR-15 Barrel: 16 ” M4 Contour Barrel with 1:8 Twist,Chambered in 5.56/.223 ,Parkerized Finish, Carbine Gas System, ANDERSON M16 5.56/.223 Complete Bolt and Carrier Group is chrome lined, made from 8620 steel, Bolt is made from 9310 steel and coated per mil spec.