Wow, case cleaning is prolly the single most talked about but least important aspect of case prep/reloading. Simple metal working; if a particular tumbling media isn't working, try a more aggressive media. Crushed walnut shells are a more aggressive cleaning media than corn cob litter and regular tumbling media is available that will clean nearly every tarnish or discoloration of brass 5 lbs. Medium Ceramic Abrasive Polishing Tumbler Media 5 lb. Rust-Cutting Resin Abrasive Tumbler Media The resin media is easier on the brass and both will leave an even, clean matt finish. You can also mix the resin or ceramic with corn cob and get clean and shiny brass...

BTW don't mention that Brasso is not a good idea to clean brass cartridges...