finely crushed walnut shells with powdered jewelers rouge... but I have always used a tumbler not a vibrator type polisher. But I would try it since it can't hurt anything. Rich, with your skills you can easily make a tumbler.
When I last built one I used a large-ish coffee can. Center drilled the bottom and installed a bolt to stick out that was held in a drill chuck installed on a gear reduction unit I salvaged from an old car power window mechanism and powered by a salvaged washing machine motor. Turned about 20 times a minute. The lid was the standard plastic lid that came on the can of coffee. It took years to wear out the lid...but it is easily replaced the next time you empty a coffee can.
I angled the can at abaout 45 degrees to keep the contents in the can during loading and unloading the brass. You can empty it quickly by opening the chuck and pouring it into one of those cat litter boxes that sift their contents ( I would recommend you only use this litter box for this purpose, because if you make it dual purpose and use it for cat litter your brass will smell pretty bad even after only one use!)
Cost: $0.00
Results: Priceless!
Media: useable indefinitely.