6" does not sound like a long barreled gun to me, LOL. I do my tapering based on the entry thimble location, and let the rest fall where it may. No abrupt transition, actually.
I figured it was one of Ed's. That a cool size barrel can't wait to see pics of your build
James, will there be a swell at the entry pipe? If so, that would be a good place to do the transition.You can also file the oct to 16 sides ahead of the entry pipe area.If I understand what you mean.T