One time my uncle shoot a deer in the forehead w/ a .22LR, it's been about 20 years ago.
It was an extreme case, he was squirrel hunting (that's why he had a .22) w/ my little brother. The deer (Spike) saw them sitting under a tree and charged my brother. My uncle is a hell of a shot, but there had to be some luck involved here. 1 shot between the eyes and him dropped in his tracks. I don't remember the whole story but he did contact DNR because deer were not in season. DNR later told him the deer had some kinda disease, I don't remember what it was exactly.