I've met Mr. 40mm on several occasions, Randy I think it is?
Very nice and knowledgeable.
At the Knob a few weeks ago the guy who has a table next to us had a M79 receiver incomplete and it was several grand. Sorry I don't remember how much.
On the flip side, at the Sharonville Ohio show last month I met a 37mm flare gun salesman who was talking out of both sides of his mouth. If you are interested in it a lot and can make it to that show you can track him down I am sure.
The multi 22 shot cartridges and 12 gauge that he had looked like they were made out of some cold roll steel or 4140 if memory serves. Fairly basic design for the 12 if you have a lathe. The 22 would require a lathe and a mill with some moderate mathematic skills or a Prototrak/Anilam (sp?) type system.