I think I will try to bump out the 28 gauge cases. I have some copper tape that I can wrap around the base ahead of rim. Could be slow going and burn a bunch of powder, but if I can get 10 cases, that is all I need for the intent of using this as a plinker and MAYBE a woods rifle.

The other choice is expensive, but maybe best. That would be to send a chamber cast to Rocky Mountain Cartridge. They would mill a tapered brass case from solid stick and have it bored to take the .562 round balls I have. Cases would be around $5 each, maybe more, but would last forever.