You have to be careful about the walnut shell media that is sold for bead blasting. It is often VERY dirty/dusty, and doesn't really clean the brass that well. I tumble about 1,000 cases a month, and I use the Lyman rouge impregnated walnut shell media. I get about six weeks, to two months out of a batch (fill the tumbler) before I have to rinse it to wash away the dust. The dust interferes with the polishing, at least for my system. When I wash the media, I have a very, very fine mesh framed strainer, that I spread the dirty/dusty media on, then rinse with warm water, until it runs clear. I then spread the damp media on an old cookie sheet, or tray, and dry it in the oven at the lowest temp (on my oven it is 170) until the media is dry, about one hour. That depends on how much media you are trying to dry, the more media, the longer you need to bake it in the oven.
Sometimes after rinsing, it doesn't really polish well, so I add just a few drops of 40 weight motor oil, to avoid scratching. If you add oil to the media, you need to brush out the interior of the case to avoid oil contamination to your propellant. However, I generally do not have a problem, as I use a minimum of oil.
