Since I'm unlikely to own a DB rifle - I mean, I could buy several very nice bolt actions for even the cost of a "cheap" double - I just have to go by what I've read. I'll eagerly listen to the advice of someone who has first hand experience with using a DB rifle as well as a bolt under adverse conditions.
Well ok it's two years later but here goes.
Never never never never use a high pressure non rimmed cartridge in a double rifle meant for dangerous game. Ask any of the serious double users and makers and they'll all tell you the same. It may not happen today it may not happen tomorrow it may not even happen next week but you will have a failure to extract at some point with a non rimmed high pressure round in a double.
I've used both Mauser style bolt guns and doubles in hunting DG and they both have their advantages and their disadvantages. But hands down in a serious SHTF situation at close range the double is king. their is nothing faster handling nothing faster pointing and nothing faster for two shots and in some cases four shots on the planet. For everything else the edge goes to a quality mauser style bolt gun.
You won't find a serious in the know African DG double gun user with a .458 win or similar cartridge in a double. That is quite simply a stupid human trick. Doubles sold in those calibers tend to go to wanna be's who have no idea what they are doing or rifle collectors who have no intention of hunting with said rifle. There are of course a few exceptions to every rule. I tend to see the odd .375H&H in a double in use from time to time.
What never fails to amaze me however, is that some of the most experienced DG hunters on the planet with literally thousands of head of DG under their belts will warn against using certain types of rifles (push feeds and M-700's in particular) on DG yet some tourist hunter is always there to defend their pet rifle simply based on the fact that they own one. It's kind of like a battered woman defending the honor of her abusive husband.
PS
When people talk about the expense of a double they invariably mention a Royal or Dominan grade H&H double in the 6 figure dollar class. There are quite a few very useable solids doubles out there for a mere tenth of that price.
That is kind of like saying "those sports cars sure are expensive" and then immediately going to the Ferrari web sight to find prices. There are many good sports cars outside of the Ferrari just like there are many good doubles that don't have Holland & Holland carved on their sides.
As far as ammo goes the .470NE is probably the cheapest of all of the NE rounds to feed. that was until this year when Ruger announced the #1 in a .450-400NE and Hornandy will be loading ammo for it commercially.
I reload for my .470 and have the cost "down' to about 4-5 dollars a round. with hunting ammo and about 3 dollars a round for plinkers.