John:
I just got replies back from Hastings and E R Shaw, both of which make rifled 20 ga blanks. My Red Label is going off to the smith on Monday if everything works out right.
I've used the new Hornady 265 grain saboted shells in my wifes rifled 20 ga and they shoot very well. As best I can tell it has about the power of a .444 Marlin. We hunt hogs for the most part and in the Florida swamps, we walk the hogs up usually, a light short double would be great.
And we have the same problem here with shotgun only seasons. As soon as the deer season closes we have to use shotguns on the hogs and I HATE buckshot.
With the Hornadys you can easily shoot 100 yards, maybe 150. And when you kill him he doesn't have a bunch of holes in him. A concern because we eat 'em.
As for the actual conversion. I'm not a smith or trained machinest but from what I can tell it's not that easy to get the barrels regulated. The rest of the project, while requiring skill and significant knowledge and care, especially in the area of being sure it's safe when it's all done, is more straight forward. The regulation part I gather is part art and part majic.