The 5.45x39 Carbine Base 16" Upper comes complete and ready to go onto any mil-spec AR 15 lower. This upper is built with the Adams Arms proprietary piston system. The piston system parts and the barrel have been treated with our salt nitride Meloniting process making them harder and more corrosive resistant than hard chrome. The bolt and bolt carrier have also been protected by using an ion bond finish. Now you have the ability to shoot the inexpensive corrosive mil-surp ammo without fear of the parts being unduly worn out. Each upper also comes with a 30 round magazine and a Wolff extra power hammer spring to ignite the older hardened primers.