Casper- you might be able to get the brass tubing that has a .0075" wall, .015" total. The tubing I'm thinking about is the fit together tubing available at many hobby stores - each subsequent size is therefore .015" smaller than the other, so they slide together.

With this sizing, there are standard sizes, so there should be a .750" outside diameter. The next size up, ie: .765" OD could be used as a liner, along with the .750", inside it- after annealing. Then, once fire formed the ID would be approximately .738" (.768" - .030" + or - a few thou). The actual diameters would only show after forming.

Just an idea. I thought the brass might be a better idea than a thin card liner or attempting to size the cases so far down just to hold a bullet or ball.

Perhaps a Paper case would be perfect?