I have the same Arizona; and, that's what I was taught: the 5.56, which is stamped on the barrel, is hotter; thusly, will also handle the .223.
I have shot both--no probs so far.
And so far, really love the gun. I'm still putting a handle on the sound--to me, it's unique. It's a kind of pinging,ringing zing.
nice reading all....