The Colt M4 Carbine is a lightweight, air-cooled, magazine-fed, gas-operated rifle chambered in .223 Remington. Designed for military use, the civilian version is semi-automatic only, while retaining the rugged reliability of the original. It features an aluminum upper and lower receiver, with a direct impingement gas system and rotating bolt. The M4 uses 30-round magazines and has a collapsible stock, giving it an adjustable overall length