Dave,
In the dozens of dents I've taken out, only one even gave me any concern that it was anywhere near the local elongation to be concerned. That one had what looked like it had been hit with a corner of something. All the rest were typical little dents of shallow depth. I am personally confident that none of these others would be anywhere near the upper limits of yield of the fairly ductile steel used in the respective barrels. Most dents are just little things. I'll give you that some severe dents are out there that may fall into what you describe, but I just don't believe anything this side of something hit with a chisile falls into what you describe. If it did, every press brake and forming die would be making scrap.
I do disagree that annealing would be the right thing. Most of the barrels I've been around were harder than annealed steels. Some up as high as in the thirties RC, some much lower. Annealing would likely weaken the barrel more than raising a dent, IMO.
But if you believe common dent removal is risky, you should indeed stay away from guns that have had them. I just don't know how you would ever know if they were done with the full treatment of restriking and light honing.
