We tested a 22lr on a mature doe skull once(hide still on) and most all bullets that hit at an angle deflected off the skull. A perfectly flat hit was better, but how likely is that to happen. If I were to even try it(not legal here), it would be neck shots right under the head. The 22LR does the same on a hog's skull, but if you shoot them in the neck it kills them stone dead.
