The M16 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed assault rifle, with a rotating bolt. The M16's receivers are made of 7075 aluminum alloy, its barrel, bolt, and bolt carrier of steel, and its handguards, pistol grip, and buttstock of plastics. It was in service most notably in the Vietnam War, as of 1965. It replaced the XM16E1, then the M16A1, in 1967. The M16A1 was especially lightweight at 7.9 pounds (3.6 kg) with a loaded 30-round magazine. This was significantly less than the M14 that it replaced at 10.7 pounds (4.9 kg) with a loaded 20-round magazine. It is also lighter when compared to the AKM's 8.3 pounds (3.8 kg) with a loaded 30-round magazine.