Hate to burst your bubble but they are the same. Only difference is the bullets used and powder charge weight used in the military loading which is designated 5.56. Cases are the same with differences only what one would expect from different manufacturers.A couple of unit converters gave me the same answer. I expected a different result because .223 ammo is smaller than 5.56. Does anyone know why a round labeled .223 is actually smaller than a round labeled 5.56?