

The rifle would later be adopted by the United States military under the name "Rifle, Caliber 5.56 mm, M16". In 1959, ArmaLite sold the rights to the AR-10 and the AR-15 to Colt due to financial difficulties, and Colt continued development on the rifle. The original prototype AR-15 was developed by ArmaLite in 1956, and is a scaled down version of the ArmaLite AR-10 rifle, chambered in 5.56x45mm rather than 7.62x51mm. The M16 rifle series is the United States military designation of rifle variants of the ArmaLite AR-15 assault rifle adopted by the US military. ArmaLite AR-15, first pre-production model, seial number XAR1501 - 5.56x45mm
