Really, a 50 BMG for hunting? Are you kidding? Obviously a newb or an inexperienced hunter who thinks bigger is always better. Since we seem to be talking elephants, let's ramble down that road for a moment.
OK. A few points to consider:
* A 50 BMG rifle weighs about 30 lbs, versus a 460 Weatherby weighing about 14. By the end of the day, that means the 50 BMG rifle weighs about 2 tons, if you can make it to the end of the day.
* A 50 BMG bolt rifle delivers over twice the energy that a 460 Weatherby does. It also has roughly twice the recoil. That is no small matter, as many guides in Africa are hesitant to let clients shoot a rifle that will effectively stun the shooter because it makes getting away from a charging animal very difficult, which in turn causes a lot of paperwork and cuts down on return business.
* A 50 BMG burns over twice as much powder as a 460 Weatherby, making muzzle blast somewhat debilitating. The fireball out the sides of the muzzlebrake can be 10 feet in diameter, and the concussion will cave in car windows at 50 feet.
* A 50 BMG has an effective range of about 2 miles, roughly 1.9 miles farther than that of the the 460 Weatherby. Elephants are usually shot at very close range, often measured in feet.
* A miss with a 50 BMG is the same as a miss with a 460 Weatherby, which is why a lot of elephants are harvested with 404s, 416s, and 458s. Some very good shooters used to use things like 300 H&H and 318 Westley Richards back when it was allowed, and yes, even the 7X57 (WDM "Karamojo" Bell).
* In summary, you don't need 13,700 ft-lbs of energy to kill an elephant unless you want it skinned and gutted at the same time. Elephants are often killed with very normal cartridges like the 30-06 during culling operations. Ivory poachers use AKs in 7.62X39. And folks used to use black powder firearms years ago because that was all there was to use. The reason you use a big gun for elephant is to anchor it where it stands when you are only feet away from it, and to penetrate to the vitals or CNS. And you don't need a $20,000 double rifle, a lot of very bright engineers designed some very adequate cartridges that come in very portable bolt action rifles that don't cost as much as the car you wish you could drive. Besides, as stated above, the only advantage a double rifle has is the quick second shot.