Does anyone know if a rock polisher can be used on cartridge brass?

Yes, they were the first machines used to polish brass by handloaders. I wouldn't use rock polishing medium, it would be too aggressive. Go to a pet supply store and buy parakeet grit, which is crushed walnut shells.

Thanks

Used one for a couple years till I needed a bigger unit and had no problems with it, they're designed to run a long time so cleaning brass is not a problem.

I now have a couple of the Dillon case cleaner units and they have worked quite well also.

Al