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220 Swift Ammo
The .220 Swift (5.56×56mmSR) is a semi-rimmed rifle cartridge developed by Winchester and introduced in 1935. It was the first factory loaded rifle cartridge with a muzzle velocity of over 4,000 ft/s (1,200 m/s). Until the introduction of the .223 WSSM the .220 Swift was the fastest commercial cartridge in the world.