Just letting some of you in on why I don't like to buy a used .223 rifle. And the difference. .223 Remington, and NATO 5.56 are not loaded to the same specifications. Each will fit in the others chamber, and fire. BUT...The NATO 5.56 is loaded at a HIGHER PRESSURE than the Standard .223. Now when you got to buy your next USED .233 exp. Winchester, Remington, Savage, ect..... Ask what they have been shooting in it for ammunition. Time, and time again, I get the answer. "The military stuff" I know not all the military surplus is NATO, but depending on were they got it, where it was made, and when it was made.....You don't know. And most likely they don't know. Most Military type Auto's like the AR-15, Bushmaster, ect are built to fire the 5.56/.223 NATO safely but I refer to the owners manual, or call the manufacture to be sure.