Let me walk you through this, Jim. The particular barrel set I mentioned was a Philly 12 ga. Fox. There was a bad bulge in the right barrel about 10-12 inches back from the muzzle (30" barrels). After much time spent putting all the visible part of the bulge back in place, the top rib popped loose from the peening. Since the ribs had to be relaid now, I removed them, and decided to go ahead and remove the portion of the bulge between the barrels. That is when the crack was discovered.
Point here is, if the visible portion of the bulge had been successfully removed without the rib popping loose I would have never known the crack was hiding between the ribs. This could have had disastrous results with ribs flying off from the gas leakage through the crack. Microscopic bore inspection may have found the crack, but how many people have the equipment to do that?
Bulges can and do create stresses in the metal that exceeds the elastic limit. Maybe a very slight ring bulge could be repaired successfully. The trick is determining when the limit has been reached and when it hasn't.
SRH
