I tumble all my spent brass in crushed walnut shells (Lizard Litter from pet supply store) but in a vibratory tumbler made for brass(don't know if it's the same as a rock tumbler). Of course they are for reloading, but the practice is the same. Adding a cap full or two of turpentine or mineral spirits to the media first helps clean them. I tumble the media with the spirits about 10 minutes, then add the brass. Tumble about 3 hours, separate brass & media, add a couple caps full of Turtle Car Wax to the media, tumble until mixed, then add brass again for another couple of hours. Brass comes out very shiny. Some folks let 'em tumble over night. Of course, buffing each case individually might get them a little shinier, but it's a lot more work, at least for me.