Not to take away from Mark's original post.

I was told by a retired gunsmith years ago to also lightly heat the barrels to get the molecules moving and then tap on the spot.
I find out what the bore diameter is right before the dent and make a steel plug that is tapered and slid it under the dent. Many times you can raise the dent without even taping on them.
As to a bulge, anything under 20" from breech is a not good. No guarantee the metal is going back to that spot.

David