The twist rate should be able to be controlled by the degree of angle of the cutter flutes. I`m going to try it with something similar to the tip of the drill bit with two cutting flutes and changing the angle. I will probably start with a 1/2 degree angle of cut on the flutes and go from there. As I said the rifling was rough but significant and when I forced a .22 pellet swaged to just a hair over bore size it does twist as it goes through the section of barrel I used. It was about a 4" piece. You could see the rifling marks left in the pellet after forcing it through. This is all still very preliminary.
We have a family member that is in tool and die and I am going to see if he might be interested in making up a couple of trial rifling bits. I may also try for a button rifling bit that would be pulled through the bore. Which ever way works out I`ll go for a 6 groove bore. I`m going to do a bit more research into twist rates and find what angle for the flutes will give the twist rate needed. I`ll keep everyone interested up to date with any results.