For $9-$10 each , Brownells offers brass laps (in four different sizes) which Brownells says can be chucked in a hand drill and used to finish the crown on all pistol and rifle barrels (when used with 600 grit silicon carbide abrasive). (See, www.brownells.com, item # 080-764-350, for example.) These things apparently don't have pilots, so I guess if you don't have a lathe or a drill press at home, you are supposed to just put your rifle in a vise and stand there lapping the crown by pressing the turning brass lap against the muzzle. I am thinking of trying to refresh the crowns on my rifles by polishing them with this. Has anyone tried these things? Is it likely that I will just mess up my rifles' crowns if I use an unpiloted tool like this?

I'm certainly no gun smith, but this method seems to be widely recommended and generaly accepted as a proper way to finish or touch up a crown. I think most people just use a round headed brass screw with the lapping compound and chuck it in a hand drill. Assuming the crown is cut correctly the ball or screw should self center. Remember you are just touching up the crown not trying to recut it.
Good shooting,
Weagle

I've used them on several guns to touch up the crown with verygood results, just take your time. I stop when I see a thin shiny line all the way around the grooves.

Rob