Well poo, the .50 BMG generates 12,500 to 13,000 ft/lbs of energy. A .416 dia. bullet wieghing 450 grs would need to travel 3,575 ft/sec to match the .50 BMG.
Now that I think about it, to get any wieght the bullet would need to quite long and the barrel would need a faster twist . I think the M-99 .50 has a 1in15" , I wonder why they did'nt go with a .45 cal ?