That's really not a ding, is it? It looks more like a pockmark, a small piece has fallen out of the barrel. A ding would be impressed and could be raised but this doesn't look like material was moved into the barrel, it looks missing.

FWIW I have a damascus barreled English gun with something similar, but much smaller, just ahead of the chamber and it passed reproof without a problem, in fact they asked me if I wanted it proofed for 2-3/4".

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- Errol Flynn