I wonder if the dust residue that always seems to be stuck to the shiny clean cases after tumbling might be more abrasive than what ever residue might be stuck to a case after firing?
Media is abrasive I guess, might stand to reason that the dust is too.
Jim, if you're tumbling in the red walnut media from Lyman, that dust is a red rouge. It is technically an abrasive, but is so fine that it just polishes, and shouldn't do anything harmful to your barrel. If you put some cut up paper towel strips in the media, it'll cut down on the dust a lot, the towel attracts the dust.
If you're using corn cob media and case polish, there shouldn't be any dust. If there is, either get new media or put a little mineral spirits in it.
