RE: Cantilever or rib vent barrel?
For turkey I would go with a vent rib and some good fiber optic clamp on sights. Or get a turkey barrel that comes with some decent open sights. I see no need for a scope on turkeys. Maybe a red dot, but good open sights should work just as well. Heck my buddy has no trouble killing them with twin beads on his 870 special purpose turkey gun.
What kind of gun are you talking about?
Paul