I always clean before I run them through my sizer die. Then I resize them and clean again to get all the lubricate off of the cases before I prime and charge them. I have quit using the corncob media just for the the reaosn I have read on here. It sometimes is hard to get out of the cases and primer pockets. I am using only the walnut media now and am much happier with it. I also use Lyman's Turbo Brite in the media to shine the brass. I buy the walnut media at pet smart and it is very inexpensive.