Can 5.56 ammunition be fired in a 223 rifle?
.223 Remington ammunition can be fired safely in a 5.56x45
rifle; 5.56x45 ammunition cannot be safely fired in a .223 rifle.
In the case of some partially imported rifles, they are marked .223
Remington in spite of having 5.56 chambers. This is done for
compliance with BATFE laws regarding importation of certain
firearms types. If in doubt about the compatibility, call the
manufacturer - they're the ones who would know best.