Wow! That is clever, beorn. I could not tell how the shaft was driving the tumbler from the video. I look forward to the improved model. This is something I in which I have a real interest as one of the possible PAW businesses I am contemplating is the small-scale production of black powder for use in black powder cartridge arms and muzzleloaders, particularly flintlocks.
I want to stock up .45-70, .45 Colt, .32-20, and 12 and 20 gauge brass shotgun shells, plus primers and wad materials for my own use. It is a plan, but I am not very far along on it. The ball mills would be one of the biggest expenses, as I want several smaller ones that I can have in a protected area and run power to them with remote switches in the power lines so I can start and start them remotely. And with small mills if something was to have problem would be limited in size plus I would not lose all capacity.
Anyway, great job. When you get the modified system going please post on it.
Just my opinion.