Uhave2:
I removed the hammer, front sight & cylinder, left the trigger assy. in place. taped off the trigger & ejector rod then stuffed Silly Putty into any hole, slot or crevice that I figured the media would get into. The Silly Putty works great, easy to remove.
Not sure what size the beads were, the fellow that owned the cabinet I used said it was the smallest size available locally.
After bead blasting I disassembled the gun and sprayed it down liberally with brake cleaner followed by CLP then re-assembled.