 The .223 Remington cartridge has a shorter neck and the shoulder is moved back slightly compared to the .222 Remington Magnum.Case capacity is about 5% smaller than that of the .222 Remington Magnum, but it was loaded to a slightly higher pressure, so the two have essentially identical ballistics.As any widely used military cartridge is guaranteed to be a success on the commercial market, the .223 Remington sold exceptionally well and the .222 Remington Magnum faded rather quickly.