I’m not sure such exists. I measured my old Reminton 511 which is pretty generic and it is .760 at the chamber tapering to .610 at the muzzle I don’t have an octagonal barrel to check. I’m almost certain they never taper.
53 posted on 09/19/2018 11:52:14 AM PDT by CrazyIvan
(A gentleman arms himself for the protection of others.)