What I did was fasten the rifling cutter(one groove) on a threaded rod, one end of which had an epoxy slug molded in a .45 cal junk barrel. The .45 cal barrel is chucked in the atlas, with an indexing pin, and power off. The shotgun barrel is clamped to the tool post base. As the threaded rod is pushed thru the barrel, the epoxy slug makes it rotate. The index pin is pulled to let the lathe chuck rotate for the next groove, when the cutter is out of the choke section of the shotgun barrel. Quite time consuming, since the cutter only cuts about .002" per pull, and the cutter needs to be shimmed out for another .002" after the first 6 grooves are cut. Much chip clearing every cut, even though the cut is about 2" long, in the choke part of the barrel. Howe's Gunsmithing has a diagram of rifling cutter construction.
