On some guns, you can not polish enough to remove all tool marks from the feed ramp without removing too much metal. Just be happy with removing any ridges that grab your fingernail. Same with the throat of the barrel. If your gun is a fairly recent commercial Colt or similar, the throat will already be wide enough. It will just need polishing. After using a dowel with fine sandpaper, you can use a Dremel with a felt bob & polishing compound like "Blue Magic" for the final gloss.