Hal, you have had better luck than I, with cylindrical tuners. You say you secure it with a brass locking nut; does your design require tools to adjust? Does the small bore, beyond the muzzle configuration pose any problems while cleaning?
I know your type tuner works because I have built a number of them, I just find my new design to be far more user friendly, easier and quicker to adjust, lighter weight, and less expensive. Why not let me send you one to try on your 6ppc? If you don't agree it is superior to what you are using just send it back. What do ya' say?
genebeggs@cableone.net
Later,
Gene Beggs