RE: ar-15 question
I have owned AR-15 rifles with both chambers. The 5.56 ammo in the .223 chamber will run a little higher pressure than it will in a 5.56 chamber, but it so far hasn't caused any pressure related problems. And the .223 ammo in a 5.56 chamber runs a little lower pressure, but the guns still have enough gas pressure to work. Seems to be a non-issue from a practical standpoint.