The first CKiller bullet with the huge hollow point cannot be meant to penetrate the skull - can it? It's not a shaped charge & would not act as one, as far as I can see as a shaped charge has a detonation component to drive a sharp metal forward through the material it contacts.
Friends of mine are butchers. Franz (Swiss butcher) uses his BRNO .22LR for dispatching cows & horses. It only works well with .22 Stingers, I assume due to the higher velocity.
The do not work against large Hereford bulls, but the .22 Hornet I gave him, with 40gr. HP's at 2,900fps, does wonderfully against the bulls.
The .22 Stinger round and Hornet only work due to velocity.