Agreed, NitroX. I would think particularly with an all 'rounder caliber like a .400 Jeffery, .375 flanged or even 9.3X74R you would want a double to be sighted in out past regulation with just one barrel for best accuracy.

My only double rifles are a 12 bore muzzleloader and a .470 NE which I really can't imagine using past 100 yards, and that is the longest distance at which I have shot either at the range. My .450/400 3 inch is, again, a Ruger No. 1.

Historically, have the longer range (e.g. 200 yard) express leaves on doubles been sighted in using one barrel or a compromise of both? Would probably be a great application for a detachable scope or folding tang sight to zero one tube for longer range work. On a SXS I would probably sight my left barrel in for longer range as I am used to choking my shotguns that way.