Interesting, while I can't say I've ever measured it myself, there's often comment about repairable bulges being appreciably thinner. Since it may not by practical to direct pressure spikes, I've wondered why all bulges aren't actually ring bulges that showed in a less than circumferential manner due to an area that was struck thinner or had some other weakness. I believe the proof process has shown that a barrel can be bulged or blown without obstruction.