In these modern times most people think of aiming for the chest, the heart and lungs. When I first heard of that as a kid I was totally confused as I'd NEVER heard of such a thing. Not only does it potentially ruin meat but the animal is not likely to die very fast. We hunted with ONLY head shots in mind, except for ducks which we purposely hunted by the flock, back when that was legal. We were meat hunters, we hunted only to put meat on the table and not for sport at all. It was considered silly and wasteful to take more than two or three cartridges out hunting. We used single shots for everything. We hunted ducks and geese with a .22, and we didn't aim at the body, just the head, as we didn't like chewing down on lead and we knew it was bad to eat lead.
Thus, no matter what sort of gun we speak of, the head shot, or better yet, just as my grandfather taught me, aim for that point in the middle of the brain where an imaginary line between the ears intersects with an imaginary line from between the eyes. And he said, be certain of your shot to the size of a dime or don't take it.
In defensive shooting things are different, I know that of course, but even then it is head shots that make the difference. Even then a head shot may not take effect in the split second that would be more comfortable in a defensive situation.
I've shot perhaps two hundred feral dogs and cats, most with a .22 but some with far larger guns. Chest shots, even with a 12 ga. are not always instant and it's not the size of the critter but the size of the fight in the critter that makes the difference.
The worst examples I've experienced where with roosters who were in fight mode, as they had suddenly decided that only one of them, out of a dozen, was to rule all the chickens we had. The fight was so insane that they attacked two of the kids in the yard so I went for my gun, like any farmer would do, to take out the harmfull critters that were loose amongst the kids. I found out a lot about fighting cocks... They are nearly immortal. I put an entire magazine of .45 fmj into a fighting rooster once, and he finally went down. However, there were still several roosters fighting and he got back up!!!!! a minute or two later and took on two more roosters!!!!!!! The fighting chemicals of adrenaline and whatever else is involved in an attacking critter can be incredible and totally unbelievable. I was unable to hit the head of the attacking roosters or I would have aimed for them, I was forced to aim for the chests and learned much...
It ended up that I had to take out the rest of the roosters by blowing the heads off of them with my 12 ga. and some #4 shot. The one remaining stayed in fight mode for almost a half hour and was ready to attack anything but me. My girlfriend at the time said the entire barnyard was ready to salute me in fear when the killing was over.
I had some similar problems with chest shooting attacking dogs and even more so with attacking feral cats. That attack mode is an incredible pain-killing situation. I found one cat, shot in the head with a .22 Stinger, about 1/4 mile from where I shot it, and it had a hole the size of a golf ball in the back of it's head. One attacking female dog took several magazines of .45 fmj and hps to the chest as she continued to come at me. She was snapping and charging me so I couldn't get a good head shot. The first magazine of .45s slowed her down but she was still snarling and in attack mode. Somewhere at about 3 to 4 magazines she went down and was crawling toward me as I continued to pump .45s into her. Finally I put two into her head, an in her weakened condition, heavy with lead, she died. I then took out my little .22 TPH, all that I had left, and looked to see what else, what other dogs, I might need to handle... at that point there were two or three other dogs that I could see, but they stayed their distance and kept moving back and forth behind cover, growling and causing me GREAT concern... happily there were no more attacks from that pack as I was down to 7 Stingers and would have had to rely on grabbing them by the throat and putting stingers into them from contact distance, and that was my hastily designed plan, as I backed away.
I think I'm starting to remember why I moved up to a shotgun in the woods back then now...
