The 5.56 produces higher pressures than a .223. So the higher pressure (stronger) 5.56 barrel can shot both. But the .223 should just shot .223.
Does anyone know of a .223 barrel having trouble after shooting 5.56.
Yup! .223 is safe in either chamber as well as the Wylde chamber.
The only .223 rifles I remember 5.56 being an issue in were the older Ruger Mini 14 “Target Model”. I have a mini from the early 80’s that has seen mostly 5.56 and even though it’s marked “.223”, the manual says specifically that it’s ok to shoot 5.56.
I’ve also heard there are bolt rifles that are .223 only but I’m not sure the make or model.