I believe the 12/20 mixups first saw the "Light of Day" peering out the chamber side of a 12ga double. You don't know anything is wrong unless you look down the chamber. "ANYTIME" you think you have loaded a gun & it snaps, check the bbl. Now this is of course much easier to do with a double, but the simple fact is, it has been ignored to the detriment of a good number of doubles. Only in extremely rare cases will a 16ga shell go far enough to get a 12ga behind it, but with a max chamber & min shell rim, it can occasionally happen.
