If you're limited to only 300-350 grains with the .50 why not go to a .44mag? A 340 grain .429 bullet will have better BC and SD than the same weight in the .50, giving the .44 the advantage, assuming you're comparing both bullets at the same velocity. You also have the perk of being able to use .44 special for plinking or reduced recoil and bullet availability should be better with the .44.
You can also fire a 630 grain .458 cal bullet from a 45-70 it will have considerably better SD than a 600 grain 12 GA slug and likely have more muzzle energy.
Last edited by JD0x0; May 10, 2013 at 08:04 AM.