Not really. It is sold as .223 because it is loaded as .223.
5.56 has a higher pressure, and requires a slightly different chamber.
There are NO and I mean zero, 55gr NATO 5.56x45 loads. The crossed circle indicates NATO spec ammo when in the military supply system. In a box of federal ammo it means nothing.
Gunlover, its NATO brass in .223 retail packages and being sold as such. In a federal ammo box it means the same as is a nato marked box. Its illegal to use the nato marking on brass if it doesn't meet nato spec. so it is 556 brass. sure lower pressure and different bullet but its nato 556 brass, military spec nato brass. not tallking about the powder or projectile, just the brass. so yet nato brass 556 brass works just fine in 223's, the manufacturers think so or they wouldn't sell it as such


















































