ArmaLite AR-10 A2 is a .308 (7.62x51mm NATO) caliber rifle developed in the 1950s and introduced in 1956. The features of the AR-10 became the M16 / AR15. The ArmaLite AR-10 has a forged and machined A2 Upper Receiver, 20 inch Chrome Lined Barrel (RH 1:11.25 twist). The ArmaLite AR-10 has an overall length of 41 inches and weighs 9.8 pounds. The AR-10 is an air-cooled, magazine-fed, gas-operated (direct impingement) rifle with a rotary locking bolt. The ArmaLite AR-10 A2 has a tactical Two Stage trigger