I have a couple of Oly barrels, one is a Stainless "Ultra Match", and the other is a plain-Jane 20 in. I recently sold off a carbine with an Oly barrel too. All are/were chambered in .223 commercial, or perhaps I should say were throated in .223 commercial.
Mini 14s had long throats, and Bill Ruger hisself said they could shoot 5.56 spec ammo. This would make sense because local Governments (read prisons) seemed to buy most of them in the old days and used military spec ammo.
