XM855 ammunition is loaded to NATO specifications. It is not intended for use in commercial bolt-action rifles chambered in 223 Remington. The full metal jacket bullets feature a steel core and green penetrating tip. Brass cases are reloadable.5.56×45 ammo derived from the .222 cartridge and was officially adopted as the standardized NATO round in 1963. Essentially, 5.56×45 as a caliber came into being because the military was using 7.62×51 and critics believed the larger round was too powerful for light service rifles, leading to rough recoil and a slower than desired rate of fire in military service rifles. Today, the NATO standard cartridge is designated as “M855”. You’ll often find it in-stock and available to shooters. We also carry a huge in-stock selection of .223 ammo for sale here. 5.56 ammo ready to ship, from the best Ammunition retailers online.