I have done a few, but the key word is polishing. I use my dremel, cloth polishing wheel and a couple different grits of clay(harbor freight or Ebay). Your barrel will get pretty warm, so I clamp them in my vise with some heavy 1/2" thick nylon blocks.
You don't want to take any real material off, so little by little and keep checking your work is the best way to learn. You could pick up a couple old barrels @ a show to practice on. I learned by doing Hi Points, so there wouldn't have been a loss anyway.