I use lizard litter crushed walnut that I buy from the pet store.
Pre treat the media with scratch and swirl remover used on automobiles (a couple ounces).
Just pour it on and run the tumbler a couple minutes to let it mix together.
Then each time before I run a batch I add about a half ounce of the swirl remover to the media and tumble to mix.
My brass is beautiful after about an hour.