Yes, Fox Mfg used a tumbler to get the shiny finish on the cases circa '72-'75. (I left Fox Mfg in Oct '75 for the final time.)
The tumbler itself looked like a small cement mixer. (And knowing Duke, it could have been just that!) The cases were polished during Second Operations, before any drilling/tapping. (I think.)
The medium used were small, chromed, spherical "marbles" w/an edge around the circumference. Memory has me thinking they were about 1/4" or less in overall diameter.
I cannot remember how long the cases were tumbled, but I do remember the noise when in operation as I walked past the tumbler on the way to/from the restroom.
Good luck in your quest.
Andre