OK...just when i was starting to get a handle on my understanding of which ARs could and could not fire 5.56, I am re-confused by my own rifle. I have owned my COLT AR-15 a3 LE/govt Carbine, for several years now. I bought it NIB for an absolutely awesome deal. Had it not been for this deal I would not be an AR owner probably. I have shot it very little. Always using .223. I was fondling it a little and putting on a light coat of oil yesterday. It was part of a special run getting 16" heavy target barrels. The receiver is marked .223. The barrel says "5.56 NATO/HBAR". For you AR gurus, am I safe to shoot 5.56?