I've had the same corn cob media in my tumbler for about 15 years now. It's long past it's prime as a cleaner / polisher. So wile I was in the kitchen shopping for reloading supplies I stumbled across a 20 lb bag of medium grain Jasmine rice. I'd heard mention of using it to clean brass befor, so I thought I'd give it a try. That stuff did an awesome job at cleaning. It didn't polish it shiny but did it ever clean up in a hurry. The only draw backs that I can see is that it is louder than corn cob, and there was a grain stuck in almost every primer hole. But for the job it did it's worth the extra time to clear all the flash holes.
Just thought I'd share
Nora