I have seen too many headshots leave the deer alive and flopping around. Part of my job for the past 23 years has been dispatching animals that have been hit by cars including deer. The only part of the brain that regulates the heartbeat and breathing is the medula oblongatta, The brain stem. If you don't sever that connection they continue to flail around. Sure you might get lucky, but a shot to the heart or through the lungs, in my opinion, is more effective a greater percentage of the time. I will let a deer walk rather than shoot it in the head. Neck shots are better than head shots, but the heart or a shot through both lungs deprives the entire brain of blood and /or oxygen ending it quicker and cleaner. A shot to the vitals has never failed. I watched an officer shoot a fawn 5 times in the head with a .357 and utterly fail to promptly dispatch it.