Are you dry or wet tumbling? I don't see dry tumbling as working with black powder. I decap and wet tumble my rifle and handgun brass after a soap and water cleaning and they come out looking new. Without doing this the heavy black powder slurry makes it hard to shine up the brass. I do not do it all the time, just when the brass is starting to look a little dull. Have not had enough of the brass shotgun hulls to bother with yet but that may change in the future. Using the SS pins and detergent with a little lemmi shine really gets the inside and primer pockets looking good. Until I decide it's time for a tumble I just use hot soap and water with a bottle brush for the inside and 4 O steel wool on the outside. Brass may not sparkle but it is clean.
