The merits of the caliber debate with modern ammunition


When it comes to the scientific test results in things like ballistic gel and whatnot, the measurable data puts the best of the best all within very minor margins.

So what we need to understand is simple, with handgun rounds, what stops the threat?

There are two ways to stop a threat - psychological and physical.

A psychological stop is when the criminal mentally gives up when they are physically capable of still fighting. Psychological stops usually happen at one of three points: when the gun is drawn, when the gun is fired, or when the criminal is hit just once, even if it isn’t a lethal or otherwise physically incapacitating shot.

With these three kinds of stops, the caliber matters little. These types of psychological stops are how .22lr derringers can incapacitate a criminal, even though a tire iron is very capable of dealing more damage than a .22lr through arm muscle. However, larger centerfire calibers (9mm/.40/.45) have a louder bang, so they have the edge up in scaring the criminal into submission.

The other type of stop is a physically incapacitating stop. This is when the criminal is shot to a point of physically not being able to keep fighting no matter how mentally motivated they are. This is a very hard thing to quantify because what incapacitates a tiny 90lbs sickly person vs a 250lbs very physically fit person vs an average 150lbs person who is hopped up on drugs is all very different.

There are different ways to physically incapacitate someone. The big ones are a “lights out” kill shot shutting down the brain, bone destruction preventing appendages from working, organ destruction, or bleeding out. Most incapacitations with handgun ammunition are through the last two - organ destruction and/or blood loss. Unfortunately, many criminals are still lethal threats while bleeding out or after their organs have been completely torn up. Sometimes bleeding out can happen very quickly, such as if an artery getting severed - people can go unconscious in seconds if one of those are hit. Even if there is a direct hit to the heart, a criminal can still keep shooting back for a few seconds. However, it is very possible to keep on living for hours after being “fatally” shot.

To further complicate things, what is determined to be physically incapacitating is different based on their weapon. For a rather extreme comparison, if someone is shot through the lower spine and paralyzed from the waist down unable to walk but their arms still work, they’re still very much a threat if they have a gun but aren’t much of a threat if they have a knife.

So what does this long analysis mean?

Shot placement is more important than bullet size or diameter. We must puncture something vital in order to physically incapacitate someone.

The bullet size and design simply increase the area of destruction the bullet creates as it enters in the body. So how can we get the maximum amount of area of destruction into a person? Well, if you do the math, 15 rounds of quality 9mm ammunition has a greater total area than 10 or 12 rounds of .40cal.

So when we look at the actual damage to the body, 9mm can actually give us greater amounts of damage to a person than .40cal or .45acp simply because we can put greater quantities of it on target.

But wait, there’s more!

Shot Placement

There’s more to a gunfight than simply creating holes in a criminal, so the discussion of “which round is best” cannot start and end with how big the holes are in a criminal - especially since we know that where the bullet hits is more important than the size of the hole created by the bullet. When we talk about shot placement, this is where things turn into a case by case basis depending on the individual. So you need to know the answer to the question, “Which gun are you fastest and most accurate with?” I’d venture to bet that 99% of people with training will be the fastest and most accurate with a quality 9mm pistol.


Thanks to the FBI, we know in about 50% of all violent crime, there’s more than one attacker. So not only do we need to put holes in the right place on one person, we need to have the ability to do the same to other people as well. This is pretty easy to objectively quantify as the number of bullets in the gun determines the winner in this category. This depends on the gun, but you ger more 9mm in a gun than a similar sized .40cal or .45acp.

Speed of the engagement

Now every shooter needs to answer another case by case question - which gun and caliber allows you to quickly put multiple shots accurately on target on multiple targets? If you’ve never practiced quickly putting multiple shots on multiple targets, then you’re not adequately prepared for a self defense encounter and need to go train - preferably in a class, force on force class, shooting competition, or all three. (I better get back on target before I go too far down that rabit hole) Each shooter will perform differently, but like the previous shot placement section, I’d venture to bet that 99% of trained shooters will be fastest in this category with a quality 9mm handgun.

Make up shots

This brings us back to the capacity question. Gun fights are fast and brutal - but the vast majority of them in the civilian self defense world are over in seconds. Thanks to the FBI we know that the average hit rate of police officer and citizen is… not as good as we would want. Even in force on force training with simunitions in the hands of very skilled shooters, there are a lot of misses. It’s understandable due to the factors such as stress, moving targets, target identification, and the like. This means that we want as many rounds in our gun as possible to give us as many chances as possible to hit the target, let alone get an incapacitating hit on target.


When we consider the amount of physical damage capable by a full magazine of 9mm, .40cal, and .45acp, a full magazine of 9mm has the greatest capacity for destruction. It’s also pretty safe to say that average and trained shooters will be faster and more accurate with 9mm as opposed to .40cal or .45acp. Finally, when it comes to having the most number of chances to hit a threat and get an incapacitory hit on target on top of that, the more rounds in the gun, the better.

There is ONE caveat to what has been said. If you live in a state with 10 round magazine restrictions, then definitely consider .40 S&W. But aside from that…

All of this means that currently, 9mm is by far the winner.

Well, I guess this means I have next week’s blog post written for Locked Back… so I’ll just copy/paste this over there and clean it up a little bit… so that’s pretty neat for me.


I still prefer .45 acp, if you use the same brand /style of bullet then compare the two the .45 will be more effectice shot for shot. The 9mm has alot lighter recoil and far better capacity, it obviously has huge advantages over .45 . Theres a reason 90% of the armed forces use it. For me ,I just prfer a bigger round for defensive use…although I do jump back and forth on this alot.


Shot for shot is a 100% useless metric through because you’re almost never going to only fire one shot in a defensive encounter. Compare magazine to magazine. My 15 round 9mm magazine has more destructive capability in it than your 10 round .45acp magazine. Or even if we compared a larger .45acp magazine, I can still go even larger than my current 15 round magazine.

Let’s take it one step further and get some imaginary data with a pretty easy to imagine results.

If we were to get on a shooting line together with five targets in front of us, I would be able to put two shots on each of the five targets faster than you would with your .45acp, and I would still have 5 rounds left in my gun. Or I’d have 17 rounds left in my gun if I have my other magazine. Or 21 rounds left in my gun if I carried a different gun.

Even if we put 4 or even 10 rounds on one target, I’d still be faster and more accurate and I’d have more ammunition left in your magazine.

The data really does not back up your preference.


What data? I prefer a bigger round. I can fire a .45 acp almost as fast as the 9mm but the 9mm does have the advantage when it comes to recoil management and a pretty significant advantage when it comes to capacity. I stand by what I said, shot for shot the .45 acp is more effective ,especially if we are comparing the best loads in each but the 9mm has a huge advantage due to weight, capacity and recoil management. Its apples to oranges ,I can give you a whole bunch of data backing what im saying too but so what? Pick what you want and what your comfortable with, I have nothing against 9mm.


This is a great write up. Here are a few points I’d like to bring up:

  1. By your metrics, shouldn’t .380 ACP, .32 ACP, 5.7x28 etc be a more effective round than 9mm? If accuracy and capacity is all the matters (while still have the bang over a .22), then by what metric do you disqualify these rounds?
  2. Capacity is… tricky. What are you loading for? I can carry 37 rounds of .40 on my belt, is that still worse off than the 17 rounds of 9mm in the gun? Capacity arguments are more dependent on the philosophy of use, since you have the chance to carry spare mags, mag extensions, etc. As well as this, capacity doesn’t mean anything if your magazine jams, and you need to clear the malfunction.
  3. The type of bullet should be taken into consideration. A hollow point .45 will always be a more effective round than a 9mm FMJ for defensive use. Again, this comes down to philosophy of use. Are you shooting big 4 legged critters? Maybe you want to use 10mm, or .44 magnum.
  4. Let’s compare muzzle stats for Federal Ammunition’s 155 grain .40 against 147 grain 9mm. The .40 is a 155gr round moving at 1160 fps with 463 foot–pounds of energy. The 9mm is a 147gr bullet moving at 100 fps with 326 foot pounds of energy. So the .40 is a faster bullet with more energy to impart into the target, with handling characteristics arguably comparable to the 9mm. Is the 9mm still a better round in this case?|undefined|undefined|359546|381520&configuration={E57E7365-12F7-4730-B220-7E212873DD66} Yes, you can say this is cherry-picked data, but what a 115gr vs 147gr 9mm? There’s no “perfect round”, and you will always give and take when you mess with dimensions.

I think 9mm is the best all-around general purpose caliber for the most new and undertrained shooters. However, I won’t say it’s the specifically best round. .22 is has higher capicity. 10mm has loads more energy. .380 auto is easier to shoot. I will continue to carry both .40 and 9mm, but I will never feel handicapped carrying the former. If carrying a .45 gets you to carry a gun everyday, then that’s the best caliber for you.


As I’ve said before, if I only had1 shot to stop a perpetrator, I’d have a lot more faith in a 1 shot stop using 45acp than 9mm.


The age old argument like the ak and ar debate

I say carry what you want too as long as yiur proficient with what you carry and realize that shot placement is key


.45 super is similar to 10mm and it is just a beefed up .45 acp round. Plus, if both expand 30% with the same ammo than .45 acp is still creating s bigger hole.


Read my two comments.

Those calibers don’t have the same penetration and expansion that 9mm/.40/.45 have. They aren’t in that same realm of almost the same with the best performing of each caliber within very thin margins of each other - .380 and smaller calibers than 9mm do not have that same level of performance with current technology.

This is how those rounds were disqualified:

.380 either under penetrated or over penetrated and of the rounds that were in the ideal FBI standard, they didn’t expand nearly as well as 9mm.

Ammo in the gun.

Reloads in a civilian gunfight are non-existent. And by non-existent, I mean, I haven’t found a single instance of a civilian reloading in a gunfight that changed the outcome of the fight.

Almost all gun fights end in one of two ways - the criminal running at the first shots or a full mag dump. There are gunfights between the two, but those two are the most common outcomes.

All of that aside, gun fights are FAST. I mean, VERY fast. Almost all (non-warzone) gun fights are over in the first volley. I’d say that most shooters don’t have a sub 3 second reload and most gunfights are over in less than 3 seconds. You want to be able to end the threat without reloading because chances are the rounds on your belt will never see action.

Eh. Kinda. Within the context of self defense, FMJ isn’t even in the consideration to me because that’s not something you should choose. Why would I compare FMJ 9mm to hollow point .40 cal when I’m not carrying FMJ 9mm?

We’re talking about the best performing rounds of each caliber. There isn’t much worth discussing comparing inferior rounds to superior rounds because I’m not putting inferior rounds in my self defense gun.

The context of this discussion has been self defense against criminals.

Go look at the end results.

The energy and velocity aren’t the only data we need to compare. We need to consider penetration and expansion as well.

You don’t have just one shot though - you’ve got an entire magazine.


With 9mm, you need an entire magazine! No guarantees you’ll get more than 1 shot in close quarters


Read my comment talking about what actually stops a threat.

This guy was shot 7 times with .45acp and still won.

.45 is not a magic want from the Harry Potter universe. A good shot placement with a .22lr will do better than bad shot placement with .45 acp.

Go watch gunfight videos. Yeah, you do have the opportunity for multiple shots. I’m not going to be in the fight and then magically out of the fight within my .2 second splits.

One shot physically incapacitating stops are a statistical anomaly - not the norm or anything that should be counted on. And of the one stop shots, it wasn’t the caliber - it was the shot placement. Of the one stop shots out there, a 9mm would have done the exact same thing as a .45 acp.

Shot placement is king.


"There is a huge amount of misinformation out today about the effectiveness of defensive handgun cartridges.

It’s true that new bullets have better terminal performance than older, less-advanced bullets. However, the performance gap between cartridges stays the same. What has changed is that the new bullets have elevated performance levels, so that cartridges that were once considered to be ineffective self-defense rounds are now thought to be acceptable.

However, no matter what you hear, remember this: A bigger, heavier bullet carrying more energy equals higher performance. That’s physics, and the laws of physics are pretty much a fixed set of rules.

Here we’ll look at some ballistic facts about the three primary defensive semiauto pistol calibers in use today—the 9mm, .40 S&W, and .45 ACP—along with the pros and cons of each. It will help you decide which is best for you. I used Barnes TAC-XPD self-defense ammo for the comparisons"


Its an opinion what actually stops! The same type of “studies” which change week to week with the weather! A larger expanding slug gives greater possibility of striking vitals than a smaller one. You may be a decent shot but in a high stress encounter, you’re probably not going to prove your marksmanship



Agreed. And that is why I think a Glock G21 would be a good primary home defense gun.


9mm is preferred by most experts due to recoil management , capacity, and cost. The .45 still has better ballistics, especially .45 super. Choose what works for you, I spend time out in the woods and its either 10mm or .45 acp for me ,although I change my mind from time to time and go back to 9mm. .40 cal looks neat too.


So many of these caliber comparisons look at 1 bullet vs 1 bullet.

That is a narrow focused look.

We need to look at the full capabilities of 1 magazine vs 1 magazine.

A full magazine of 9mm will do more total damage than a full magazine of .45 and 9mm will give you more chances of hitting that vital part.


If you’re carrying a gun, you should be carrying a spare magazine, for the same reason you carry a gun-because you don’t want to need it and not have it. They’re easy enough to carry (mine is right next to my leatherman and and in front of my tourniquet on me belt). This is especially true for people who conceal carry single-stack handguns. Not everyone carries a full-size double stack. Again, this muddles the concept of magazine capacity.

It’s a great chart for comparison, and I check it every now and then as they add new tests. You can find rounds in each caliber that perform better than rounds in other calibers, but what I see is that performance within each caliber depends greatly on the manufacturer and grain. Not to mention the potential differences in velocities due to barrel length (a 5 inch fullsize may likely have better balistics than a 3 inch subcompact), but that’s a whole new argument.


Yes 1 bullet! Ever clear a house? You could encounter a threat charging you around any corner! You may not get 1 shot let alone multiple! Better know how to use your hands. It WILL happen a lot faster than in your “practice” drills


Am I the only one who read that and thought “wonder what the DPS calculation is…”. :cowboy_hat_face:

/video game nerd


These young whippersnappers today got a lot of book smarts but not much real world experience…