my brother in law shot a buck this weekend that had abnormal antler growth on one side (sorry, no pics), upon cleaning the head we found that in the back of the skull was a perfectly round indentation, around 0.75cm in diameter and the same deep, it only just had penetrated the skull with the inner point of the hole, leaving an opening of about 1mm at most to the brain cavity. There was all kinds of strange 'stuff' coming out of the hole when cleaning it.
it was suggested that it was from another bucks antlers during rut/fighting, but I think it was a .22 bullet that failed to penetrate the skull.
ps. I'll try to get picture or two to share!