This upper offers a M4A1 11.5" Remington 4150 Chrome Moly Hammer Forged Chrome Lined barrel a 1:7 RH military twist rate. The Flash hider is a A2 this is for PISTOL OR SBR USE ONLY. It is also made of chrome-moly steel and HP tested. Our barrels are Mil-Spec or better. The upper is a Mil-spec A4 and at a length of 11.5" it's pretty darn short. We recommend a 55gr or 62gr bullet for best accuracy. The front sight is a A2 F-Marked with bayonet lug.