Longbow, I had to go back over my notes and read some books to polish up on what I know (or don't know) about Paradox and bore guns. G Wright has a chapter in his latest edition of his book about shooting paradox guns. He does an in-depth study on original guns and mics bores and slugs but says nothing about rifling twist or depth. A couple of things that I have learned.(1) The paradox slug needs to be bore size or slightly under bore size. (2)The slug needs to be a BN of 10 to 12 to be able to swedge into the rifled choke with out damaging the barrel. WW are usually 9BHN. (3)This type of slug shooting apparently works with a faster twist than we would normally calculate for a bullet that size. I do wonder if this is because of the slow velocity. When calculating twist the calculator says 1100 too slow, they want 1300 which is impossible with black powder. (3)The only actual specs I have found on paradox rifling is that one person said his rifling is .008 deep which would make the choke .016 or modified. (4) there was company that was doing paradox rifling in , I think a 60" twist but have since discontinued the service. "Darlington Gun Works" (5) I don't know squat.
I have a half finished rifling bench that I need to get out and finish so I can continue my quest for a paradox or bore rifle. I have been working on this for a while. Probably the best option at my age would be to buy one, then I would be shooting next week!
Here are some barrels makers, that I need to contact"
http://thegunworks.com/
They specialize in "Bore" rifles and even offer a 2 bore!
https://www.lothar-walther.com/
Just found this site, it is interesting that they offer shotgun blanks, and BPCR blanks
Bob Hoyt PA'
Bob has a little one man shop going and does all kind of barrel work on obsolete barrels, relines re bores, sleeves, and makes new barres . I have had him rebore and make barrels for me before, TOP NOTCH. He doesn't do the Net tho. I can get you his #