Great pix of the cutters.It blows my mind that the most simple appearing or primitive looking cutter could do what it does.Would love to see this in person one day.Hopefully! It would be interesting to hear from the operators how the two different cutter styles perform. That top and bottom appear to have zero or slightly positive rake and the middle one is negative rake. More a scraper than a "cutter". Throughout the riffling process, did they ever use a rougher and a finisher or did they just touch up the bit when ready to finish?
Cool thread, hope to see more!