Perfect for building your custom AR15 upper group. Comes with a properly installed M4 barrel extension. All barrel sub-assemblies are properly headspaced. Chambered in 5.56mm 16.1" Barrel Length M4 and Lightweight Tapers Carbine Gas System Length 1/2-28 Threads 1-7 Barrel Twist Salt Bath Nitride Finish Mfg: Cmmg
