This Mark 12 Mod 0, ready to shoot 5.56 Complete Upper is equipped with a 18" Douglas 416 stainless steel barrel 1-7 twist with a fitted bolt and commercial carrier, flat-top receiver, PRi flip up front gas block front sight and rear sight, rifle length gas tube, a Gas Buster charging handle with big latch, and a OPS inc brake and collar. The system also comes with a Gen III Rifle length carbon fiber free float forearm in Black finish and a full length top rail with PEQII removable rail section.