what can be shot in what 5.56

[gcrookston]

But a chamber marked as .223 should not fire 5.56? Is that how it goes? 5.56 chambers will handle both, but .223 chambers should be used for .223 only?

This always confuses me......(not a difficult task)

Correct. 5.56 is loaded to a higher pressure. 223 lead in is shorter. Often burst primers are the most often result (although catastrophic failures have been known in older .233 guns).