The Annoyed Man wrote:I would amend the above to make sure to only buy brass-cased ammo. I know that plenty of people shoot the steel-cased varnished stuff, but the .223/5.56 case doesn't have enough taper to use that kind of ammo reliably. I've seen WAY too many fired steel cases stuck in AR barrels that wouldn't extract for love or money......some times so badly that running a rod down the barrel and trying to tap the case out won't remove it. Then you need a gunsmith with a chamber reamer. Brass cases OTH have natural lubricity and are very good at extracting cleanly.
Steel cased ammo is fine for AK pattern rifles because the case has a pronounced taper and extracts easily.
I've had several friends bring steel cased coated .223 and .556 to my place to shoot in their AR's. All of them jammed after the barrel got hot. It may be the coating melting and sticking to the barrel, or it may be something else. But stick with brass unless you like frustration.