Anything that will give the "coup-de-grace" (even a .22 rimfire if legal) will save you from a possible wrestling match with only your knife or gun-butt if you don't re-load before approaching. But to hunt "first shot" in my state requires what game biologists suggest -- a minimum of 500 foot-pounds delivered to the target. The further the target is, the bigger the loss in velocity -- I could bore you with Newton Physics -- Won't do it. A .50 handgun, 8-inch barrel, round ball, won't have 500 even at the muzzle. A conical might, just barely, but less at 25 yards. Not to say it hasn't been done, though. But now for a "coup-de-grace" it would be adequate. Also for smaller incidental targets. Maybe even close-up two-legged predators. Do I hear "dueling banjos" ringing in the distance?
"When you see the smoke on the wind, look for me."