I always shot my traditional MLs over snow to see if they were blowing out unburned powder. I don't believe you can overload a ML with powder, but you can with projectile(s). I think, the extra powder will just blow out, unburned, and a heavy lead load, combined with lots of fuel will cause pressure problems......Busta, please correct me if I'm wrong.
I shoot my .50 huntsman with two 50 gr. Tripple Seven pellets and a 470 gr. Maxi-Hunter. It shoots well and should do an elk just fine. I've never tried 3 (150 gr. total) There's about a 3 foot drop with that 2 pellet load at 300 yards, and I don't think that will improve much with more powder. I'd plan on getting up close and personal. Pete