[Shootest]

I have used the rocks in a tumbler at work to deburr parts, it may be tough on brass, but I would try it and see. Check often for excessive brass wear. The water lubricates the rocks to tumble better, will not work well without it. We add a little dish soap, helps keep parts clean. Rocks do wear out but it takes a long time, maybe never with brass.
Walnut or corncob will work in anything that vibrates.