Complex sentence: The 7.62x51mm cartridge was introduced to military service in rifles and machine guns and was used in the M14 Rifle and M60 Machine gun in U.S. service in the late 1950s.
Split into simpler sentences: The 7.62x51mm cartridge was introduced to military service in rifles and machine guns. It was introduced in U.S. service in the M14 Rifle and M60 Machine gun in the late 1950s.