Short and sweet: the 5.56 and the .223 are the same bullet (.224 diameter) but the brass case and primer are different. The brass is thicker on the 5.56 and the primer is less sensitive. yes, the 5.56 is loaded to a slightly higher pressure, but not a significant one. So, you can safely fire .223 in a 5.56 chamber.Which is better 5.56 or 223?
There does seem to be more options in .223, but good deals and a variety of loads can be found in 5.56 as well. Also, if you choose to interchange the two cartridges, you can more safely shoot a .223 cartridge in a 5.56 barrel. In that case, the 5.56 might be a good choice because you can have more choice in ammunition.Is 556 same as 223?
The exterior (physical) dimensions of .223 and 5.56 ammunition are effectively identical . 5.56 ammunition may be loaded to higher pressures than .223 ammunition. 5.56mm chambers are dimensionally larger in certain critical areas than .223 chambers. Given the same ammunition, 5.56 chambers will have lower pressures than .223 chambers.