Another +1 with Spike.T's sage advise.
However, I have owned one double .375 H&H belted (Merkel) and had no extraction problems.
Chose it foolishly thinking it would be my do everything rifle and so, I had it claw mounted/scoped.
Now, almost 13 years down the trail and 4 safaris later, I would not scope a double, and I generally would recommend flanged cartridges for your double, even though it gave me no extraction problems.
It even showed excessive pressure signs with the factory ammunition it was supposedly regulated with but, never left a cartridge in the chamber.
Likewise today my only double is a Heym in .458 Winchester with ejectors and so far, no problems with it either.
All that being said, I still prefer flanged cartridges for doubles, because as someone already mentioned .. Murphy's Law is always lurking about.
I recommend that you have a good look at the Heym PH model in 450/400 caliber and learn to shoot it with open sights.
The recoil is about like the .375 H&H but slower.
I bought my Heym .458 because it was about 4 thousand bucks less than the same model in 450/400 (found both rifles used at the same time) but some day when I grow up, I plan to have a proper 450/400.