The M16 is the original US military service rifle adopted in 1964, chambered in 5.56x45mm NATO. Originally designed by Eugene Stoner at ArmaLite, it was adopted following controversial trials that replaced the M14. Early variants used a direct impingement gas system. Type: Semi-Auto Rifle Action: Gas-Operated Caliber: 5.56x45mm Capacity: 20 Year introduced: 1964, USA Weight: 7.9 oz Overall length: 39.5" Status: Active Military use: Yes Intended use: Military, Service Rifle