338x74R
On my Chapuis, the Rifle was factory regulated with the iron sights. I have two scopes in rings for this rifle, one a Leupold 2.5-8 and a Swarovski 1.5-6x42, both in Chapuis Pivot mounts. With either scope the rifle regulates very well shooting as good as most bolt actions to 200 yards from field positions. I have taken a coyote at 271 yards, with witnesses on film, measured after the shot, and a Kudu at 300+ yards with witnesses also on film.
If I had a double rifle that would not group both barrels together good enough for shots at animals at 200 yards I would sight in the scope for the most accurate barrel and use it like a single shot at that distance.
Or if your rifle was like my Chapuis and you must fire the right bbl first to get good groups, then I would sight in the scope for the right bbl.

I cannot understand why there is some resistance to using a scope on a double rifle.

My Chapuis balances and handles better than any scoped bolt rifle. The stock is perfectly suited to scope use.
I have made several shots on game with the 9,3 and scope that I would not even have attempted with iron sights.
I can somewhat see how Ray might have some resistance, as he, like Methuselah, is 969 years in the past, but JOHAN is European, HE should know better.

EVERY double 40 cal. and under should be fitted with a scope in QD mounts.