Re: Cleaning dies with stainless media/tumbler?
Oddly enough... I tried cleaning a couple dies one time in an ultrasonic cleaner. Got some bizarre looking 'burn' marks on the exterior finish; looks like someone scorched them with a hand torch or something. I don't know if it was whatever chemical I was using as a cleaning solvent at the time, or something else... but I don't plan on cleaning any more dies in the ultrasonic machine any time soon.
Personally I wouldn't try cleaning your dies in the tumbler with SS pins, either. Haven't tried it, but it just seems like too many things could go wrong, for relatively little gain over cleaning by hand. If you just want to clean the gunk out of the inside, spray some M-Pro 7 or similar gun cleaner on a 3" patch, put it over a .410 or 20 gauge brush on a short stick and swab out the inside of the die, followed by another dry patch - done.