I have used Mothers wheel polish. I mix a big handful in my media. Shines the crap out of brass. Kinda mix it together with your hands. After a little bit of tumbling, you'll never know its there.
If you have them in your area, Ace Hardware carries Flitz. I was reading about polishing the bolt on the Savage 93R17 and Flitz was mentioned, been using it since 06 with no problems.
You can buy it at several places like Natchez or Midway and from Flitz. You can look it up on YouTube.