There are a few arguments in the firearms world that just never seem to die. “AK vs AR” is probably the most famous, and we might try to tackle that at some point when I feel like beating my head against a brick wall for 5000 words. Anyway, second only to that is “9mm vs .45ACP”, and that’s the one we’re going to look at today. The argument more generally is about “light and fast” vs “slow and heavy” as it pertains to handgun bullets. So we’re going to examine this whole concept, look at some of the ideas people have had about it, link to a couple of articles I’ve found on the topic, and then finish up with my own thoughts.
A caveat: This article is all about defensive shooting. If you have no interest in using firearms for defense, this info won’t really mean much to you. It might even hurt your feelings or make you uncomfortable. Fair warning.
Let’s start by defining a few terms. “Stopping Power”, as I use it, is not the same as “Knockdown Power”, a concept you might have heard of before. “Knockdown Power”, or the ability of a bullet to physically knock an attacker to the ground, is a silly idea when it comes to handguns. Here’s some relevant physics: Every action has an equal and opposite reaction. What this means for us is that the energy pushing the bullet forward is matched by energy pushing backwards against the gun. As my friend Isaac reminded me yesterday, “Force” is equal to mass times acceleration, and acceleration is change in velocity over change in time. I don’t want to get too off topic here, but what that means is that you feel less force when you slowly accelerate your car to 60 MPH than when it comes to a sudden stop against a tree. The mass of the car stays the same, so the difference comes in how fast you go from 0-60 vs how fast you go from 60-0. Same thing applies to bullets, but the mass of the bullet isn’t equal to the mass of the gun plus your arms, shoulders, chest, etc. so the same energy pushing the bullet will push that bullet faster or farther than it will push you. Make sense? So, if you think your bullet is going to knock down a bad guy, you’d better be shooting a gun that packs a heck of a whollop. That means big rifles, maybe big shotguns. Maybe. Even then, it really depends on how quickly the bullet changes velocity in the target. Even a big round that goes straight through someone without slowing down much isn’t exerting a lot of force (not a significant change in velocity of the bullet over time). A big round, moving very fast, that hits an armored plate in a vest might knock someone down because the bullet goes from real fast to a complete stop very quickly against that plate. All clear? Okay, so if we’re talking handguns (except maybe some giant-ass hand cannon like the S&W 500 magnum), and we’re not talking about people wearing armored plates, we’re not even close to anything that is going to exert enough force on a body to knock it down. The rounds, once they penetrate the body, will begin slowing down, but they don’t stop immediately so the change in velocity is happening over a longer period of time than when the bullet hits an armored plate. The size and shape of the round and what it encounters along its path will determine how much it slows down inside the body. This is why expanding rounds are more effective than ball ammo. When a hollowpoint expands, it increases surface area, which means it will slow down more quickly, exerting more force.
If someone starts talking like a regular .45 ACP hardball round shot into an unarmored attacker is going to have “Knockdown Power”, they’ve just confirmed that they are not your best source for firearms info. “Stopping Power”, however, is the ability of a bullet to cause someone to cease aggressive action. Maybe that means they run away, maybe it means they just stop moving towards you but remain upright, or maybe they actually do fall to the ground? That’s fine, but we need to be clear that the bullet is not knocking these people down. That’s a meaningful distinction. It’s important because Hollywood likes to show dudes getting shot and flying backwards through plate glass windows. Real bullets don’t do that. If you’re in a defensive shooting and you expect that your rounds will cause a violent, visible response in your target, you will likely be disappointed. Many, many people who shoot someone in self defense don’t even think they hit the person, because there’s so little immediate physical reaction. No flying backwards with limbs flailing, no explosion of blood from the entry wound. That’s what you need to be prepared for, rather than thinking your gun has “knockdown power” and one round is going to put your attacker on the pavement whether he likes it or not. Now let’s talk about what actually needs to happen in order to get someone to stop attacking you.
There are three (maybe four) ways to get someone to cease aggressive action. One is what we call a “psychological stop.” This means that the attacker still has the physical ability to attack, but has stopped because they are choosing, consciously or unconsciously, to stop. This could be because they’ve got extra holes in them now and have decided that they don’t want any more of them. It could just be that they are in pain, and choose to stop to avoid any further pain. These stops are very common, but unreliable. Even a slap to the face could be enough to stop some attackers, if they’re not particularly invested in the attack. Does that mean that a slap to the face is your best defense? Obviously not. The next two ways are really one way, but we’ll split them out for clarity. The first is massive bleeding leading to unconsciousness. If the body loses a sufficient volume of blood, there will no longer be sufficient pressure to get the blood into the brain to keep the whole thing moving. Since the brain is still the big kahuna in this scenario, the “massive bleeding” stop is still essentially a central nervous system (CNS) stop. Anyway, this is why people are generally advised to shoot for the “high center chest” area of an attacker. There are a lot of bleedy bits in there. More importantly, there are bleedy bits that are big enough and important enough that if they are damaged, unconsciousness should follow relatively quickly. Unconsciousness due to blood loss would be a physiological stop. Once a person loses enough blood, they’re going to stop attacking no matter how dedicated they are. How much blood a given person has to lose to fall unconscious is an unknown, unfortunately. And as you’ve probably heard, there’s generally enough oxygen in the brain to continue voluntary function for 10-15 seconds, even if the heart were to suddenly disappear entirely. The third way to get a stop is with direct damage to the CNS, meaning the brain or spinal cord, generally. This can provide the most effective stop, as it is possible to get a “puppet with the strings cut” response. Police snipers, I’m told, train to hit the brain stem so that there isn’t even the possibility for a reflexive trigger pull as the body is falling. Direct damage to the CNS means that signals from the brain no longer reach the muscles. Voluntary physical action within the affected systems is no longer possible, and the effect is immediate. So that’s a good thing, but it’s almost as if your body knows how important these parts are and surrounds them with tough bone. Yeah, it’s a bummer. So while CNS shots are super effective, they’re also harder to make. The maybe fourth stop is a skeletal stop, I guess you’d call it. The idea is that bones and muscles work together to allow movement. A bullet fired into bone could cause that bone to cease providing a stable platform for the muscles to work against, thereby disallowing voluntary movement with the affected body part(s). An example of this is the “pelvic girdle” shot, advocated by some people in the defense world. Essentially, a gunshot to the pelvis is supposed to shatter the pelvic bone, which will render the attacker unable to use his leg(s). Here’s why this is a maybe. First off, I’ve heard from several knowledgeable sources that handgun rounds do not shatter the pelvis. They merely poke holes in it. Also, if your attacker has a ranged weapon, having him on the ground at distance from you isn’t actually rendering him incapable of causing you further harm. It might just be making him a smaller target and giving him a more stable shooting platform! So that’s why it’s a maybe. It’s possible that a shot to a certain skeletal structure could do sufficient damage to disallow movement of the limb, but it’s nothing close to a guarantee.
Okay, so those are your three (maybe four) means to get an attacker to stop attacking. When I talk about stopping power here, I’m talking about the ability for a given round to achieve the goal of stopping an attack by means of one or more of those mechanisms. Now to be clear, every single firearm that I’m aware of has the physical ability to achieve all of these stops (except the maybe fourth one, which is another reason why it’s a maybe). Even the lowly .22LR has sufficient power to penetrate into the chest cavity and damage the aorta, or to damage the carotid artery in the neck, and it could certainly damage the CNS if fired into the right spot. As for psychological stops, we’ve already explained that almost any physical stimulus can achieve one if the attacker is really not all that into the attack. So clearly, any firearm will do that job if the attacker cooperates.
I’ve now spent over 1000 words just getting to the big point here: It really doesn’t much matter what handgun caliber you use. All of them are functionally identical, especially as compared to rifles and shotguns. Handguns are inherently underpowered tools, and the differences between them are very small when compared to the difference between handguns generally and rifles or shotguns generally. There is one caveat to this, though. I think that it’s important to use a handgun round with significant penetrating power. While a .22, .25 or .32 can potentially cause enough damage to vital organs to produce a stop, they’re also much more likely to be stymied by heavy clothing, distance, intervening materials (wallboard, windows, etc.). So my personal opinion, and take this for what it is, is that your primary carry gun should be something in .38 SPL or better (Maybe .380? That’s borderline in my opinion). If you want to carry a tiny pocket gun for backup that’s chambered in .22, .25, or .32 then I think that’s okay. Chances are very good that 2-3 good hits from even a “mouse gun” would be enough to stop any but the most dedicated attackers. However, as defensive shooters we’re not too keen on putting our faith into “chances are”, as a rule. This is also where we need to quickly explain the difference between a gunshot wound being lethal and stopping the threat. As defensive shooters we are not shooting anyone to kill them. We are shooting to stop them from killing us or our families. If the attacker won’t stop until lethal damage is caused, then lethal damage, unfortunately, is required. Keep in mind, however, that just because something is lethal doesn’t mean it will necessarily stop an attack. A .22LR round the the heart might kill the attacker in a few days, but it might not be doing enough damage, quickly enough, to cause the attacker to stop in the timeframe necessary to save your life. That timeframe is generally “Right Now” in case you were wondering. Attacks happen quickly, and defensive stops need to happen very quickly to prevent harm to yourself or your loved ones. So, while you might get a psychological stop out of the small calibers, and they might even be plenty lethal, they may not be enough to force a stop in a dedicated opponent. But what about the other calibers? Certainly a 38SPL and a .44Mag are vastly different when it comes to fight-stopping effectiveness, right? Not really.
But don’t take my word for it, read this article by Greg Ellifritz: An Alternate Look At Handgun Stopping Power
Look at the data. It’s pretty clear, I think. We’re talking about minor differences between these rounds, overall. These are differences in degree, not in kind. Even comparing the .22 to the .44 magnum we don’t see astounding differences. Basically, everything is within about 20% of each other at the very most. We’re not seeing a steady, consistent rise in effectiveness as we go from smaller, weaker rounds to larger, more powerful rounds. What that says to me is that people don’t like being shot. Maybe they like being shot with big bullets a little less than with little bullets? It’s a bit moot, though, since the one thing we can never know is how a given attacker would have responded to another caliber. Proponents of the .45ACP will point to times when the 9mm has failed to stop an attack, and cite it as an example of how the 9mm isn’t an effective defensive round. Unfortunately for them, this isn’t good science. We don’t know that the same person, in the same situation, if shot in the same places with a .45ACP would have stopped his attack. We can’t know that, and that’s the only thing that could definitively say whether one was “more effective” than another for a given situation. Incidentally, we also don’t know if a person who was effectively stopped with a .45ACP would have been similarly stopped with 9mm rounds. It’s entirely possible that he would. There are too many variables, and too little reliable data for anyone to ever truly unravel all of it. That’s just reality, so we’re doomed to compare apples to oranges forever.
Here’s what we can take from that data, though. Most attackers required 2-4 shots to cease aggressive actions. The caliber matters less than getting multiple good hits. Which rounds will allow you to get multiple good hits? Generally those that produce less recoil. So you need enough energy to provide for sufficient penetration to damage vital organs (in case the psychological stop isn’t happening) but not so much that you can’t get quick, accurate hits. As with so many things in life, we’re seeking a balance. For me, the 9mm Luger provides the best balance of capacity, penetration capability and rapid-fire accuracy. Even with a compact 9mm, I can still carry 14 rounds, and I can get good hits on target quickly. For me, that’s the right balance. I also carry with 124-gr +P rounds, so I’m adding more weight (standard is 115-gr) and more velocity to the standard 9mm loading.
Now, just to complicate matters, I want to bring your attention to a another article. This is a direct response to the article linked above, written by Grant Cunningham. I’ve linked to him many times before, because I love his writing and his thinking. Here’s the article: A Different Take on Handgun Stopping Power
He has some concerns with the statistical rigor of Ellifritz’s piece, but still prefers it to some other famous discussions of the topic. Cunningham’s conclusions are pretty similar to Ellifritz’s when all is said and done, too. Most handgun rounds will do the job with 2-4 good hits, and the bigger, beefier rounds are not necessarily the only way to get an effective stop. Here’s Mr. Cunningham’s conclusion: “Bottom line: pick your gun based on your ability to use it efficiently, practice frequently and realistically with it, and you’ll be far more prepared than the average gunshow denizen who loudly proclaims that all good self defense calibers must begin with ‘.4′.” Here’s Mr. Ellifritz’ conclusion: “No matter which gun you choose, pick one that is reliable and train with it until you can get fast accurate hits. Nothing beyond that really matters!”
Seems pretty consistent. Train hard with whatever you intend to use for defense, because fast, accurate hits are what matter.
If you’re really interested in a much more in-depth examination of everything that goes into stopping power, you should definitely read Grant’s Stopping Power Series. He covers all of the things I’ve covered here and more, and has a much greater depth and breadth of knowledge. So if you’ve got the time and the inclination, I highly recommend reading through the whole series
A couple things you might have heard that I hope we’ve debunked:
- “All good defensive calibers start with a 4.” – grant even mentions this one in his conclusion, quoted above. It’s incredibly common in the firearms world. The people saying this are claiming that .40 S&W is the smallest caliber that will be an effective defensive round. Do the data support this? Clearly not. This is, to be blunt, bullshit posturing. It’s the sort of thing that people say when they haven’t done any research on the topic, but when they want to sound very manly. Apparently reading isn’t manly?
- “Carry the biggest caliber you can handle.” – This one is squirrely. If by “handle” you mean delivering fast, accurate shots under stress consistently, then this is at least sort of okay. The problem is that you don’t have to carry the biggest round you can handle to be effective. I can shoot a 10mm quite well (I even got some darned good hits with a .500 S&W magnum the other day), but I carry a 9mm because I shoot it faster and more accurately at speed. I bet I’m not the only one who experiences an improvement in shooting performance by stepping down from my maximum caliber, either. This is where that balance comes in. Personally, I want to end any defensive encounter as quickly as possible. If I can get 2-3 good hits with quality 9mm defensive ammunition in under 3 seconds (and I can), that’s better to me than getting those same hits in 4 seconds with a .45ACP (I also can). In this case, the biggest caliber I can handle isn’t the best fit for my goals as a defensive shooter.
I’ll leave you with my conclusion, which will echo those of the other gentlemen: Your success in a defensive encounter is much more about training, mindset, speed, shot placement and ammunition quality than it is about caliber. Pick a gun you can control, practice with it a lot (under stress when possible), and carry it loaded with quality ammunition.