Most shops that do re-rifling use single point cutters and some form of Pratt and Whitney rifling machines. Broaches have been used for rifling, but mostly for military guns where only one caliber and twist justifies the expense of the broach. Button rifling is not suitable for contoured barrels because the rifling depth will vary as the wall thickness changes. I would think that a back bore of 0.010", except for the last 6" or so behind the muzzle would allow for a Paradox type rifling, and the bullet mold could be made to fit the back bore diameter. If the barrel walls are thick enough, that's the way I would go.
