My Dad was in the tombstone business and I learned about sand blasting from the ground up. In the shop we used a carborundum (black) media as it would not turn to dust as sand would. We used a hard silica sand in the sandblasting machine to do lettering on existing monuments in the grave yard. That fine hard silica sand is great for sand bags but my best guess will scratch the heck out of brass if left in the tumbling cycle for a extended period of time. I personally use crushed walnut hulls with a case cleaner that I get from MidwayUSA that is not a RCBS or Lyman but does a great job of cleaning and POLISHING my brass. If you just want to clean the brass just use crushed walnut media without the polish for an hour or so and not worry about scratching up your brass. Those are my thoughts.
Lemmon from Rural South Carolina.