First of all, forget about caliber for the remainder of this discussion. There is no handgun or rifle that you are going to easily carry around or keep ready in your home that can 100% guarantee the incapacitation of an aggressor. There are too many real-world instances where a .22LR dropped one bad guy in their tracks but several .45ACP rounds to the chest did not do the job on another bad guy. Factors such as the physical and mental state of the involved combatants play a much larger part in survival and fatality rates than the ballistic charts of the involved bullets. Your job is to make leaks in the hydraulic system - leaking air in and leaking fluid out. Breaking bones, removing mobility, or causing large wounds are all bonuses, but don't count on them.
Let's start our assessment of shot placement by taking a look at some of the standard targets being used in training today:
Have you seen the above target before, or something similar to it? Chances are that you have, and that your overall goal was to hit the 'X'. You may have even heard it referred to as "Center Mass", or the center of available mass. But think of anatomy, and where that 'X' is located. Putting all of your shots in that location would certainly make most attackers think twice about continuing their actions, but we're not looking to make most bad guys reconsider their attack - we want to train to do everything in our power to make all bad guys cease all aggressive action as soon as possible. Shooting them a bunch of times in the mid-section is not the way to get this done, nor is scoring our hits based on a numerical value. I don't care about a high-score in a defensive situation, I care about stopping the threat, which means putting my shots in the 'Juicy Goodness' - that area in the high chest where lungs, heart, and spine are located. Notice that there are also no target areas outlining the head or neck area, which are sometimes the best or even the only available shots. This is not a target that I would consider to be a good target for use in training.
On the other hand we have the VTAC targets, or 'Skeletor', as we lovingly refer to them.
There are several reasons why a target such as this is a good choice for effective shot placement training. First of all, even though it shows the standard scoring rings in dashed lines, it clearly highlights putting your shots in a small, concentrated area right in the location where you are most likely to make holes in the hydraulic system. Training to keep your shots tight and also to keep them in the high chest will increase your chances of being able to do that in the real world. You will also notice the presence of bones and also that the target is realistically shaped, therefore showing and not giving credit for hits outside of the Juicy Goodness which would not be effective, or which may over-penetrate due to their lack of hitting anything substantial. A scoring box around the head is also shown, and while it does not include the neck (which it should) and is a little large for the actual neutralization zone of the head, it is one of the more realistic target areas when compared to the target areas of most other paper torsos. Shots to the head can certainly be effective if done correctly, which means to place them between the eyes or into the eyes to increase the chances of a round entering the frontal lobe of the brain and potentially shutting down the central nervous system,which stops the body altogether. The downside to head shots, as we're about to discuss, is that when they may not penetrate the hard skull, and can even ricochet off of the curvature of the skull. Shots to the face - mouth, cheek, chin, etc. - may not stop an attacker at all, while similarly placed shots to the Juicy Goodness would most certainly have a greater effect. As for the box around the pelvis, that's another discussion for another time.
Let's look at the case of Daniel Tice, an Akron, Ohio resident who shot and killed his wife back in 2009 and then holed up in his basement with his 4-year-old son. SWAT officers were eventually forced to make entry on the house, and after failing to subdue the 6'1", 280 pound man with beanbag rounds fired from a shotgun, they went to lethal force as Tice raised his own weapon towards police officers. A SWAT officer fired a single round from his 9mm MP5 sub-machine gun, which struck Tice in the forehead, subduing him long enough for officers to make the arrest. The amazing part, however, is that the round did not enter Tice's head - instead, it just glanced off. It could have been the angle of the shot, or it could have been a plain ol' hard-head, but either way, this guy survived a 9mm round to the forehead - a few inches lower, however, and the shot would have put this scumbag into the dirt for good. He recovered from the wound and was convicted of the murder of his wife.
So without proper shot placement, head shots are not necessarily the way to go. The skull is a small target, a hardened target, and it moves around easily, so the answer is to shoot Center Mass when possible, right? It's a larger target, often it is also a softer target, and shots there increase your chance to incapacitate a target - assuming that you get your shots in the right part of Center Mass, or what we call the Juicy Goodness. Now consider the case of Angel Alvarez, who survived 21 shots to the body by NYPD officers back in 2010. Bullets fired by officers struck Angel's hands, arms, legs, jaw, and abdomen, but not one single shot struck anything vital, such as the heart, lungs, brain, spine, or any arteries. These are officers who are trained to shoot for Center Mass, which by all accounts they managed to hit, but what they failed to do was strike anything that mattered. Was the suspect incapacitated? Absolutely, and after he healed up in the hospital he went to trial for his crimes. But that's not the point - the point is that if were just you against Alvarez, and you only had the chance to fire a few rounds into the Center Mass of your attacker, and they did not strike anything vital, then your attacker may not be swayed by your measly show of force. In the case of Angel Alvarez, a forensic pathologist was quoted as saying, "More than 20 gunshot wounds is a record. Of course, the real issue is where you get shot. One bullet can kill you, but believe it or not, a body can survive a lot of bullet wounds." Here's Alvarez, alive and well just a few weeks later, on his way to court.
Shot placement is everything. In the end, it doesn't matter how many shots you fired, how quickly you fired them, or what caliber you used. What does matter is whether or not the shots that you fired were placed effectively into an area where they would do the most damage and have the greatest chance of telling your attacker or attackers that you'd rather just buy more ammo than be a victim. You will fight like you train, so train like you want to fight.
Stay Aware, Stay Safe, and Train Hard.