I am sure that this is common knowledge but what "media" is used to clean brass cases in a tumbler. I have seen walnut media and corn cob media. Are both used? Does each have a purpose or does each do the same thing. I am thinking that the walnut would be for really dirty cases and the corn cob media would be used to bring the cases to shiney new condition. I am sure that this is a very basic question but I am new to this so any advise would be helpful. CHEERS, notasniper