Small caliber has nothing to do with it. A smaller round with higher fps, can do more damage than a larger caliber; not to mention the various types of 'additional' damage rounds out there; hollow points, black talons, etc.
Smaller rounds also have a tendency to bounce off of bone and create more internal damage not seen by the naked eye.
Just sayin'.
.22 through your descending aorta bleed you out just as quick as a larger, the 556 you'll have tumble and cavitation with secondary 'shock' injury to organs.
Seen all kinds of injuries with various calibers. seen a woman survive a 357 to the dome, seen a dude pop his top with a .22 semi auto
pistol, maybe I should have differentiated it by saying such, versus .22 rifle