Many people, be they new to the shooting sports or old timers, often forget that, while the 5.56 NATO and .223 Remington use the same bullet and case, therefore, look identical, are not the same round and are not interchangeable. While the .223 Remington can be safely fired, in any gun designed for the 5.56 NATO round, the reverse is not true and not only unsafe but very dangerous.
See the attached PDF, for details.
Gary
556 NATO vs 223 Rem.pdf (740.7KB)