Wondered if rather than crimp the case mouth that a slightly deeper seated ball with a card wad over the top with a centre hole cut in the top wad and then the wad fixed in place with hot-glue around the wad to seal it to the case wall. The ball should be able to run free but well fixed until fired. I use the hot-glue method when I load shot in brass cases but with a complete top wad. It saves wear and tear on the case mouth. Lagopus.....