Over the years, I have been asked a number of times what my handgun caliber choice is & why. It’s not a simple, nor fast question to answer so I’ll make an attempt to provide a comprehensive answer here.
The rounds you will find by my side most often are some form of expanding 9mm hollow points. They are not +P’s or +P+’s, just your regular octane leaded type. Before I go on let’s get the definitions for mechanics of projectile wounding out there:
Now that that’s out of the way, let’s discuss how a person or animal is incapacitated by projectile wounding. There are really two ways projectiles incapacitate a target, the first being massive hemorrhaging (blood loss). This could take some time to incapacitate as there are a number of variable factors: At what rate is blood loss occurring, what physical state is the target it, is the target pumped up on drugs, what is the mental state of the target, etc. The second way to incapacitate is to shut down the central nervous system (CNS). Shutting down the CNS is instant lights out! To summarize, you have two incapacitation options: you can wait for the target to drain and pass out or flip the CNS switch and be instantly out.
Let’s talk about draining the target….
If you want to drain a bucket full of water the bigger the hole you drill in the bucket the faster the water will flow out the bottom. The same thing for humans and animals, however there is no significant difference in flow rates between hole sizes in .35”, .40”, .45”. Yes I know there IS a difference but do the math. Let’s say the bucket has a bottom that’s 1.8m2 (average body surface area of a male human is 1.8m2 ), 19.3ft*2 , or 2970in*2. If you poke a .45” hole in the bottom then .0054% of the surface area is allowing water to escape. If you poke a .35” hole in the bottom then .0034% is allowing water to escape. Personally I don’t think their is much difference between .0034% and .0054% in relation to the human body. After all it’s only 0.002%!!!
There are lots of people who carry .45acp’s because of its “knockdown power” (a retarded term that I’ll dispel later), and because it’s “gona punch a big hole in someone”. What they don’t take into effect is how much recoil you now have to deal with and how limited you are on ammunition. There are also people who say they would rather have a bigger round so their chances of hitting a critical CNS spot are higher. Let’s do the math folks, a .45 is only 0.093 bigger than a .357, so you have an extra 0.0465” on either side to hit that critical CNS spot. THAT’S NOT MUCH AT ALL! So in order to get .002% more surface area and an extra 0.093” of diameter you’re adding MUCH HIGHER RECOIL and LIMITING THE NUMBER OF ROUNDS YOU CAN CARRY! Call me nuts but why the hell would you want to do that! Penetration? Yes penetration would be a good reason to consider. The FBI did some extensive tests a number of years ago, the penetration data from 9mm & .45 ACP shot into ballistic gelatin are below.
124gr Speer Gold Dot Penetration: 12.6” FBI Test
230gr Speer Gold Dot Penetration: 16” FBI Test
As the test data shows the extra weight of the .45 ACP round enables the round to push deeper into the gel then the lighter 9mm. This is a good thing seeing that most American’s are fat… oop’s I mean obese. So depending on what angle your target is at when rounds are in the air you might need all the penetration you can get, especially if you’re shooting for center mass and not trying to shut down the CNS. Penetration is also something to consider if you might have to shoot though barriers, windows, drywall, car doors etc. Speed is a good thing, a 9mm 127gr going 1050 is spanked by the .357 Sig (also a 9mm bullet) that’s traveling on average of 200 feet per second faster. Keep in mind that for most folks a good 12” of penetration will get you through the arm and find its way to the heart. Is 16” better? Yes. Is it necessary? It depends on the situation.
Now let’s talk about shutting down the CNS. This can be done by putting a round into the brain housing group (head) in the brain stem. This is a rather small target when compared to the upper torso. If you’re taught how to shoot correctly you know to keep shooting until the target drops. If you’re attempting to shut down the CNS with a head shot you might miss….. That said, wouldn’t you want to get back on target faster for a follow up shot? Would you rather deal with the recoil of a .500 S&W or the recoil of a .22LR? If I’m trying to poke holes in a target that’s small and moving I’d much rather deal with as little recoil as possible while sending a round down range that can penetrate the target and get results.
Ok onto “stopping power” now…. a term that each and every time I hear it I know the person who just uttered said words has no clue what they are talking about. I’m going to insert some work done by the FBI here to save time:
“Physiological factors such as energy deposit, momentum transfer, size of temporary cavity or calculations such as the RII are irrelevant or erroneous. The impact of a bullet upon the body is no more than the recoil of the weapon. The ratio of bullet mass to target mass is too extreme.
The often referred to “knock-down power” implies the ability of a bullet to move its target. This is nothing more than momentum of the bullet. It is the transfer of momentum that will cause a target to move in response to the blow received. “Isaac Newton proved this to be the case mathematically in the 17th Century, and Benjamin Robins verified in experimentally through the invention and use of the ballistic pendulum to determine muzzle velocity by measurement of the pendulum motion.” 4
Goddard amply proves the fallacy of “knock-down power” by calculating the heights (and resultant velocities) from which a one pound weight and a ten pound weight must be dropped to equal the momentum of a 9mm and .45 ACP projectiles at its muzzle velocities, respectively. The results are revealing. In order to equal the impact of a 9mm bullet at its muzzle velocity, a one pound weight must be dropped from a height of 5.96 feet, achieving a velocity of 19.6 fps. To equal the impact of a .45 ACP bullet, the one pound weight needs a velocity of 27.1 fps and must be dropped from a height of 11.4 feet. A ten pound weight equals the impact of a 9mm bullet when dropped from a height of 0.72 INCHES (velocity attained is 1.96 fps), and equals the impact of a .45 when dropped from 1.73 INCHES (achieving a velocity of 2.71 fps). 
A bullet simply cannot knock a man down. If it had the energy to do so, then equal energy would be applied against the shooter and he too would be knocked down. This is simple physics, and has been known for hundreds of years.  The amount of energy deposited in the body by a bullet is approximately equivalent to being hit with a baseball.  The tissue damage is the only physical link to incapacitation within the desired time frame, i.e., instantaneously.
The human target can be reliably incapacitated only by disrupting or destroying the brain or upper spinal cord. Absent that, incapacitation is subject to a host of variables, the most important of which are beyond the control of the shooter. Incapacitation becomes an eventual event, not necessarily an immediate one. If the physiological factors which can contribute to incapacitation are present, even a minor wound can result in immediately incapacitation. If they are not present, incapacitation can be significantly delayed even with major, survivable wounds. “
Ok so if you’re still with me I hope that you have learned something. That way next time you’re on the range or in a gun shop and you see some guy toting a 1911 and spitting out nonsense like “back in Nam” “the .45 would lift a gook of his feet” or generally discussing “knock-down power” you will instantly identity him as a buffoon.
Long explanation of why I carry a 9mm…. in short, It recoils less, I can poke more holes exactly where I need them- faster and I have more rounds onboard should I need them.
Additional notes……. Hollow-points (HP) are designed to expand at a certain velocity, thus if your hand-cannon launch’s said projectiles at a slower velocity they might not work as designed. Also keep in mind that if you clog a hollow point with clothing, or other materials it might not expand. Hornady recently came up with its Critical DutyTM line of ammunition that’s pre-clogged! They designed it so that it would perform predictably in most barriers shot during the FBI protocol. DON’T EXPECT a HP round to do magic! You’re only poking a hole in a target…. and IF the HP round does expand to cause a larger permanent cavity you don’t want to be sitting around with your thumb up your ass waiting for a target to bleed out. In closing if you can’t find a 9mm that fits your requirements (due to hand size or concealability) ensure that you carry some form of ballistic protection….. A .22 in the pocket is better then nothing!