I polish my fired cases for a few hours to get any grit off of the cases that might scratch the dies. I use walnut media, and add polishing stuff when the walnut wears out. And it does wear out after a while. With the addition of polish, you can run the same media until it turns BLACK. Media is so cheap, though, it's not necessary to keep it that long.... After the cases are resized, trimmed, chamfered, and ready to prime, I tumble (vibrate) them for another hour to get any lube off of them. Never tried the corncob stuff, but I heard it's good.