It's not so easy to find pictures of proof house failures, but the CIP does have a short video, in the 'proof' category, of failures. The reason I use that as an example is because a proof house, particularly if they show it, should have followed their procedures in which the barrels were fully measured and inspected prior to firing proof loads. In other words, free of obstructions.
Anyway, most of the shown failures appear to be twelve gauge guns, and chances are they would be thought to be obstruction failures. One picture in particular shows a 'banana peel' muzzle, lowest barrel pressure(?), blow up. Chances are the first thought would be someone stuck it in some mud or snow.
Maybe the topic gun was an obstruction, maybe not. A side thought on 'tapping down' a bulge. Material would have thinned when it was 'stretched' to a larger surface area, but the material is still there. Not likely at all, but theoretically it could be returned to where it was originally. Finishing would likely take more off, but if decent thickness remains, there're probably some unique guns to make the attempt. It's probably more common to raise a dent, the same thing in reverse.
