You don't really have to build much of a machine to do the rifling. This is an old muzzleloading rifle maker's method I read years ago: If you have a longer barrel than you are making with the correct twist...never mind the caliber, the bigger the better for this...you can make a long "bench" with the rifled barrel one one side (Call this the "donor" barrel) and the blank on the other. A long rod is run through the donor barrel and a hard lead slug is cast on the rod end closest to the blank. A pull handle is set up on the other end right at the muzzle. The actual rifling rod is then attached to the donor barrel's rod. The far end of this rod has a bore diameter - .001" wood, brass or even lead piece attached, with a pocket in it at the correct rifling pitch angle to accept your rifling cutter. The cutter is raised by shims, usually thin strips of cigarette paper.
Yep, the description is rough, but I'm sure you get the idea.
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