[Andonius_99]

they *should* be...but there are rare occassions of the hotter .223 being too much for the 5.56 innards...

Other way around...556 is too hot for 223.

[Gilbo_3]

good catch Sir...more coffee needed i reckon...

[Dead Corpse]

There are two difference, powder and chamber leade.

5.56 NATO mil-spec uses a slightly faster powder. .223 chamber dimensions, where the bullet nose is spaced to the throat of the rifling, is a couple thousand^ths tighter than the 5.56 chambering.

This means pressures can spike dangerously in a .223 chamber when shooting mil-spec 5.56 ammo.