Damn it's crap to get old! The brain farts seem to just get more pervasive!

You are correct, the barrel being fired always recoils UP, BACK, and AWAY from the other barrel!

I have always had all my scoped doubles zeroed in at the same center POA as my irons, except for elevation, and I have no more trouble hitting a Muledeer, or elk at 250 yds, than I do with a single barreld rifle of the same caliber. A preperly loaded rifle for the regulation of the rifle, will consistantly post hits in the kill zone at 250 yds with either barrel! There is nothing wrong with zeroing the scope for only one barrel,if that is what you want to do, but that turns the scope into a specialized sight, that can't be depended on the replace a broken, or severly bent iron sight bead. I'd bet you I can hit your $200 Stetson hat at 250 yds with my 9.3X74R double rifle, with the scope zeroed in the center of the composite group!