Shot a 460 S&W a couple years ago at a gun shop w/ indoor range that was trying to demo it and sell it I shot it using the previous owner's "downloaded" reload ammo that came with it. Not sure grains, power, powder or muzzle velocity. The damn thing sounded like a high pitch booming laser cannon and spit fire like a flamethrower, hence I dubbed it "laser-flame thrower" because such a name is just as ridiculous as the gun itself. The only thing more ridiculous than what I've told you so far is the recoil. My wrists hurt for a week. Thankfully it was the end of the shooting session anyway. Now that was the smaller 460 using downloaded ammo. Please note I can shoot a 44 magnum and hit steel targets at 1-200 yards no problem.
The honest to god truth is that if you want to defend yourself from something that big requiring the 460/500 then bear spray is better, and if you want to hunt something that big there are dozens upon dozens of center fire rifle calibers that will do the same thing delivering more or less same muzzle energy but shoot a lot easier.