Matt
Raising a dent is a relatively simple process.
I have hardened and polished plugs in .001" steps which fit on a rod, so they can be slid up under a dent. The first thing is to get the bore clean - and I mean clean. Everything must be clean.
I find which plug will slide up under the dent with a little pressure, then I take a little brass hammer - also very clean, as is the outside of the barrel - and gently start tapping around the edges of the dent. As soon as the next plug can go up under the dent, in it goes. The process continues until the dent is gone.
If the dent does not come with a gouge or cut into the finish, the finish is usually not disturbed.
If it did, well that'll need a re strike and polish and new brown or black.
You have to realise that a dent has stretched the barrel wall, and part of the art (for want of a better word) is correctly working the metal to get it back where it belongs. This is where the plugs have a decided advantage over the hydraulic tools.