A short piece of wooden dowel about 1/2" in dia. and 4"-5" long wrapped with medium grit sandpaper (#240) will do a nice job. Be careful to check frequently as you go. Like Eldeguello suggested, a dollar bill should slide EASILY between the barrel and wood when you are done. Also, don't forget to seal the sanded area with a little urethane or the like after you are done. Keeps moisture out of the unfinished wood.