If I were young enough to start a new project, I think I would go with the original chambering. I have a 24 ga/5.6x35R Vierling cape gun and in searching for ammo or components I remember finding enough to shoot the gun. I believe brass cases are available and since they are thinner could be loaded with heavier loads than commercial paper/plastic case ammo. It is Ky John's project so he can do whatever he wants to do, but I don't think I would try to turn down 28 ga insert to fit the 24 ga chamber. I believe it would be easier to to bore or ream the chamber a little larger, then "Loc-Tite" a close-fitting tube into the chamber, which would then be chambered to 28 ga. It is a safe bet that he is a better machinist than I am, so maybe he wouldn't ruin as many inserts as I would trying to turn them thin enough to fit a 24 ga. chamber.
Mike
