[/quote]As one of the people who was working in that original thread, I have one question for you:
Do you have a way to get the shells up to the firing chamber (a carrier)?
That one snag kept everyone working on the project from finishing, I think I just threw away the carcass of the gun I'd built last break because it wasn't getting finished. Though I did keep the plunger and springs, which I might be using on a similar, but much simpler, project.
The bottom chamber with the spring will hold the carrier. The ramp will let the shells go into place.