The Colt M16A1 XM177 is a usa-made select-fire carbine chambered in 5.56x45mm NATO, introduced in 1963. Primary use: Military. Type: Carbine Action: Select-Fire Caliber: 5.56x45mm NATO Capacity: 20 Year introduced: 1963, USA Weight: 86 oz Overall length: 39.5" Status: Discontinued Intended use: Military