5.56X45MM NATO Ammunition For Sale. 5.56×45 ammunition got from the .222 cartridge and was formally taken on as the normalized NATO round in 1963. 5.56×45 is a type that appeared because the military was utilizing 7.62×51. Pundits accepted the bigger round was decisive for light assistance rifles, prompting unpleasant force and a slower than wanted discharge pace in military help rifles. Today, the NATO standard cartridge is assigned as “M855”. You’ll frequently track down it in stock and accessible to shooters.