Notice even at the bottom there is room for the ball to at least exit the chamber.Yes you are right... Both terms have been used. Ever had it happen? :) I did only one time because I did not take the time to grease my loads. I was very lucky because I was firing an 1861 navy colt reproduction. It just happens to have tapered relief indentations on both sides to let the ball come out unrestricted yet deflect it away on the side it happened. Never really thought about the frame design shape until that happened. :)
Notice even at the bottom there is room for the ball to at least exit the chamber.