cth350:

"...it's metal shards in a tumbler."

VERY interesting.
btw...I've done the simple green, brake cleaner, metal brushes (and even the green scrub pads). The parts are squeeky clean...but they still have a very dulled and darkish look to them. It's that original shiny'ish new metal look that I'm after. That's a real bummer if it turns out that bead blasting won't do it.