So I was waiting for leather to dry a little and thought I would fiddle with this.
The removed material at the bottom needs to be the diameter of the cartridge (in this case .429" -44 mag) The oval punch should be close to that plus the thickness of the leather doubled (.429 + leather doubled) The stitching down the case wall needs to be measured with a couple strait edges holding the leather and bullet down to a flat surface. In my attempt, my punched hole is a little too long. The stitching holes I just eyeballed the radious going under the bullet.
Knowing these measurements I think I could build a pattern.
Then the stitching on the back piece I think would be like a normal piece except the radioused part under the bullet might need to be punched during assembly?
On a bottle neck case, Ill probably have to work that out but I think the oval hole might need to be higher?