I would contend that, in the 21st Century, a DG rifle MUST have a scope on it.
Lion (if the Obamunists and the cost ever allow us to hunt them again) and leopard are often shot in low light conditions, requiring precise shot placement when it is difficult to line up iron sights. Buffalo often require shooting precisely through openings in the bush. In fact, Boddington has written that anyone using a double rifle with iron sights will forfeit 40% of his or her shot opportunities.
Hippo often have only part of their head above water. Crocodile? You must hit an object smaller than a tennis ball from dozens of yards away. As for elephant, you want to place a bullet precisely into a (mostly) non-moving target.
The only time I would NOT want a scope would be following up a wounded leopard, something I have never done. The solution is to scope the DG rifle but use QD mounts and make sure the iron sights are reasonably zeroed.
The only wounded DG I ever had to follow up was a wounded buffalo. It never occurred to me to remove the scope and the final shot was about 30 yards away, with insurance shots about 10 yards closer. The scope caused me no problems.
Make sure your rifle fits, though, so that when you look at something, close your eyes, bring up the rifle, and then open them, your cheek is on the cheekpiece and you are looking through the scope at the object.
