Oh, what the heck. Strap it into the vise and crank up the Bridgeport. We're giving you way too much to think about. Miller is right about the muzzle area, but I suggested drilling a hole farther back. That's what I would do. Good luck with the project. The swamped rib sounds like a good idea. Boss and Purdey build pigeon guns and some bird guns with no rib. A friend has one of the Purdeys and it is a wonderful gun. You could do it that way. Murphy