Which Handgun To Choose: 9mm, .40 S&W or .45 ACP?

6 mins read
Handguns or pistols on old wood texture weapons for self defense.
Handguns or pistols on old wood texture weapons for self defense. Source: Depositphotos

Everyone looking for a handgun inevitably faces several challenges when choosing one. Even if you can narrow down your extended list to a few brands with a reliable reputation, technical questions are a bit more complicated. The reason for it is that there might be some untrustworthy manufacturer who skimps on production, but the gun’s technical characteristics are never to blame. Nobody’s going to say that .45 ACP pistols are innately worse than the rest of the handguns, simply because that’s not true. The difference between types of actions, calibers, frame materials, and all other features is not in quality but preference.

Every handgun configuration exists for a reason, and your goal is to find the one that works for you. You could probably gather all the technical questions you have and head straight to the local gun store consultant, but why bother walking if you can find everything on the Internet, right? In this article, we’ll take a look at handgun’s most popular calibers and point out their similarities and differences, so that the next time you walk into a gun store, you’ll know what to look for.

What are 9mm, .45 ACP and .40 S&W?

Technically speaking, two of those names refer to a cartridge type, and one can be used to refer to a caliber. However, more often than not, people use the name 9mm to refer to the 9mm Luger cartridge, which also has plenty of other names because this is how things work in the firearm community. Interestingly enough, while .45 ACP and .40 S&W are handgun exclusives, 9mm managed to travel through a number of bores, including that of a carbine and even a submachine gun. More experienced but not necessarily better, 9mm Parabellum (yet another name) is currently the most popular handgun cartridge, in the service of about 60% of the world’s law enforcement agencies. 

All three are rimless centerfire cartridges that share the handgun ammunition winners pedestal. An expected achievement for those that have been around for more than a century (9mm and .45 ACP), and quite an impressive accomplishment for the cartridge that only appeared in the 90s (.40 S&W).

The origins of the contestants are quite different as well. The 9×19 Parabellum (that’s the official name) was developed by an Austrian firearm designer Georg Luger in 1901 for his own semi-automatic pistol. The cartridge’s low-cost production and impressive performance have resulted in its popularity. It was the primary submachine gun cartridge during WWI, adopted as NATO’s official sidearm cartridge in 1955, and remains the FBI’s standard cartridge even after a brief period of disgrace.

The .45 ACP (Automatic Colt Pistol) was invented by an American firearm designer John Moses Browning in 1904 for his prototype Colt semi-automatic pistol. After passing military trials with flying colors, it became the standard-issue sidearm ammo for Colt M1911.

The .40 S&W cartridge was developed as a joint effort by Smith & Wesson and Winchester in 1990 to meet the FBI’s need for a more effective defense round after the Miami shootout of 1986. This motley crew has managed to conquer the affection of law enforcers, military personnel, and civilians alike. Now let’s look at their technical characteristics and figure out how they are different. 

Technical Differences: 40 S&W vs. 9mm. vs. 45 ACP

Bullet Diameter

That is the primary difference between the cartridges and calibers that doesn’t allow using all types of ammo interchangeably. The number in the cartridge name refers, in particular, to bullet diameter and not to the cartridge length or case diameter. It also doesn’t have a direct correlation with gun performance: .45 ACP is not better than .40 S&W simply because the number is higher. To clarify things – the bullet diameter is measured in hundreds of an inch. As you can see, 9mm doesn’t follow the suit because it was originally developed in Europe. 9mm equals approximately 0.355 inches, the shortest diameter of the three (which doesn’t prevent it from being the most popular handgun cartridge). While not determining the cartridge’s performance directly, the bullet diameter influences other characteristics of the round. It also determines the width of an entry wound, which is one of the impact assessment criteria. 

Stopping Power

Stopping power is a relatively subjective characteristic because it cannot be precisely measured. This concept has never been quantified and is generally referred to as a cartridge’s ability to stop a self-defense situation. That can happen in two ways: either the attacker abandons their plans or gets injured so badly they no longer pose a threat. The first scenario might happen if the attacker sees that you are not defenseless, while the second one is highly variable. Stopping power might be determined by combining such characteristics as muzzle energy, bullet weight, and penetration.

Muzzle Energy

Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm. It is influenced by such parameters as bullet weight, propellant quality, and chamber pressure. Even though there are rounds with different bullet weights and, consequently, different muzzle energy, the tendency for the three cartridges is as follows: 9mm cartridges have the highest muzzle energy figures, followed by .40 S&W and .45 ACP.


Muzzle energy and penetration power are directly dependent. The thing with penetration is that you don’t want your bullet to pass through your opponent and potentially harm something or somebody else. At the same time, you want it to penetrate deep enough to inflict sufficient damage. Cartridges with higher muzzle energy tend to penetrate deeper. If you have a high muzzle energy pistol and don’t want your shots to pass through, it is vital to choose the right ammo. Jacketed Point Hollow (JHP) ammunition won’t allow over-penetration since the hollow causes the bullet to deform when it strikes the target, expanding the wound channel and making it bigger and messier. Full Metal Jacket (FMJ) ammo, on the other hand, has increased penetration property and causes neater wounds.

As you can see, the stopping power is hard to catch and question whether it is superior or not. 9mm pistols shoot light bullets at high muzzle energy, resulting in deep, narrow wounds. The 45 pistols are the opposite since they shoot heavy bullets at lower muzzle energy, causing a wider permanent wound channel. The difference between the potential wound diameter of those two cartridges is almost .10 inches, which might seem like a little, but when trying to stop an assailant, every tenth of inch matters. It might be the distance by which the shot missed a vital organ, which could have led to more severe injury and faster resolution of the self-defense situation. Your safety is at stake, so approach this issue seriously. Oh, and .40 pistols are the middle ground between the two: wounds wider than 9mm and deeper than .45 ACP.


This characteristic has nothing to do with inflicting damage, but it influences your accuracy and fire rate consistency. We would gladly give you an Eagle Eye diploma if your first shot turned out to be the decisive one, but more often than not self-defense situations are not resolved that quickly, not in your favor at least. Numerous studies (and common sense) show that stress has a heavy impact on shooter accuracy. Shot placement is the most crucial factor that determines the outcome of an encounter. And recoil can significantly hamper it. Moreover, the anticipation of recoil affects your accuracy as much as actual recoil does. That’s why everybody prefers handguns with the lowest recoil possible. 9mm pistols win this competition as they can boast the triad’s lowest recoil. Breaking the usual tendency, .45 ACP pistols take second place since they shoot heavier rounds at subsonic velocities and have lower chamber pressure than .40 S&W pistols. They are said to have the most notable recoil since they shoot bullets, that are slightly lighter than those of .45 ACP, at higher velocity. High chamber pressure only adds to recoil tangibility. 

Magazine Capacity

Magazine capacity returns the simple tendency of “the smaller, the higher”. This is quite reasonable since there is only so much space in the magazine and many cartridges willing to claim it. The smaller the bullet, the more cartridges the magazine can fit. Standard Glock 21 magazine houses 13 rounds (.45 ACP), Glock 22 magazine fits 15 cartridges (.40 S&W), and Glock 17 in 9mm has a 17-rd magazine (lives up to its name). Don’t underestimate the importance of magazine capacity, as many of your shots are likely to miss the target in critical situations. The more tries you have, the higher your chances to succeed are. 


Final Thoughts

Looks like it’s time we answered the very question we began with: which gun to choose? Instead of saying “Listen to your heart” and “They are all just great”, we recommend you think about why you need it. Are you looking for a concealed carry handgun to never be taken aback? You will benefit greatly from a 9mm pistol. Many polymer-framed light pistols have all the benefits of a 9mm: low recoil and high magazine capacity. Do you need a home-defense handgun to store in your nightstand?

Then consider a full-size .45 ACP pistol. Since the weight is not an issue, you will have a heavy-impact self-protection firearm with moderate recoil. Is there a place for .40 S&W in your everyday life? You could say so. Even though many law enforcement agencies that have been using .40 S&W pistols for quite some time are ditching it for a new generation of 9mm ones, this type is by no means bad.

It’s a solid middle ground between the two with maybe unjustly punishing recoil, but people wouldn’t use it if it were that bad. The .40 S&W pistol might become your trusted companion on a shooting range, on par with two other fighters that were mentioned and many others that didn’t find their way into this article. 

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