Well, that's certainly an interesting choice; not one that comes up every day here, and we get some crazy **** from time to time.
Case capacity with VLD style bullets...you'll give up some, and yes, the magazine box will limit you. I don't know the exact amount, but I own a .460 WBY and the magazine box will hold, at most a shell that's probably 3.8" long or so. The other problem with the round is headspace; almost has to rely heavily on the belt. Those things aside, it would work, but I'd keep it to zero freebore, and a soft angle [say in the order of 1 degree, to 1.5 degree lead angle.] Awfully large bullets, going to be spendy, and for the range intended....? But what the hell, right? Keep in mind with a 28" .50 caliber barrel that's actually going to shoot worth a hill of beans, weight will be hard to keep at 15lbs. If I were asked for some input, I would recommend utilizing the .338 caliber--it's big enough to kill anything on this continent [and really anything anywhere with no %$&*-ups], brass supplies will be much more affordable [for what you'll spend on a lifetime of brass, you could damned-near buy a stock, or 2/3 the cost of a rangefinder, or.... But, if you're set of the 50 Peacekeeper, yes, it'll work, chambering will be the most critical aspect with regards to performance {if you have to, you can always use the weapon single-shot style}. I'd think about using bullets of 700 grains and lighter, perhaps even the 683gr military ball bullet--those choices will help keep velocity up, and chambering/magazine complications down.
That design really wasn't built for zipping speeds, it was designed for long-range use on armored convoys if I'm not mistaken; it's supposed to be more quiet than something like the big fifty, because it uses less powder, and fast burning powder {less muzzle preassure}. Hope that helps; maybe some more expertised fellows will hop in here, as I've not had one of these chambered before.
