I actually knew a guy who had an Robarms M96 rifle chambered in .223 that would "overpressure" whenever he fired 5.56 out of it but not .223. Nothing catastrophic, but this rifle is designed so the barrel can be easily removed if you press on a latch and firing 5.56 out of it would cause the barrel to slip off of the latch and fall off of the rifle. It was working just fine with .223 though.

It is more of a statement to the flimsy design and construction the rifle itself than anything else as we figured that it was the pressure felt at the gas port was what was causing the barrel to jump out of the rifle and not a failure of the bolt, which remained safely locked and did its very important job of supporting the case head under the firing pressures. But it was a pretty hilarious way to tell that the rifle operated at higher pressures when firing 5.56 compared to .223.