I have an 1887 Parker Hammergun with a ring and slight bulge about 12 inches in front of the chamber. Also have a 16 ga S. Grant with a inside ring appearance a few inches in front of one chamber. I attribute it to wads sticking after a misfire. I peened the Parker bulge back to normal and have shot it quite a lot without any changes.
The answer of course is: Who knows?
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