A scope can be useful for making a shot on a bull in a herd. As compared to open express sights. I swapped my double 450 for the guides 416 Rem, 700, scope sighted when trying for a buffalo in a herd while hunting elephant. But no older mature bulls s didn't fire a shot.

Some extra magnification ie 1 to 4x might be useful. I doubt more than 4x is needed on anything a .400 shoots. I've used my 30-06 with a 4x to 250 metres well. Up to 400 metres used but wouldn't normally at least on a costly trophy fee.