You need to keep in mind the possible variation in the regulation with the extra weight of a scope. I have a 9.3 with a 1.75x 5 Zeiss it will not shoot anywhere near the open sights. Nor will it shoot a good group.

My 450/400 has a Leopold 1.75x6 and it shoots exactly the same with the open sights.

I think the difference is the weight proportionate to the weight of the rifle. My 9.3 is only 6.5 pounds without the scope and the scope is heavy. The 400 is 8.5 pounds naked with a light scope.