The M4 carbine is a shorter and lighter variant of the M16A2 assault rifle. It is an air-cooled, direct impingement gas-operated, magazine-fed carbine chambering the 5.56x45mm NATO cartridge. It has a 14.5 in (370 mm) barrel and a telescoping stock. The M4 is capable of firing in semi-automatic and three-round burst (like the M16A2 and M16A4), while the M4A1 is capable of firing in semi-auto and full automatic (like the M16A1 and M16A3).