Pistol Caliber Guide

.22lr, .357 Magnum, 380 Auto, 40 S&W, .45 ACP,  9mm para, 10mm Auto, there are so many pistol rounds available today that most new shooters are left dumbfounded when deciding on one for a new gun. For that matter, should you decide on a caliber first or a firearm and then look at available calibers? What do these numbers mean, and why should you care? Why are some calibers listed in metric units while others are in imperial units? 

Who knows? I do. And soon, you will, too. Because I’ve assembled a quick-and-dirty guide to the six most common calibers in the United States. So buckle up. We’re going on an ammunition adventure together!

This is an aspect of firearms that many people take for granted. We hear about 9mm this, or 45 that, and don’t give it a second thought. But have you ever wondered how a caliber is defined?

A firearm’s caliber is measured by the inner diameter of the gun’s bore or barrel. For some calibers this number also includes a second number that defines the cartridge’s length. For example, 9mm luger is sometimes written as 9x19mm, which designates the round as 9mm in diameter and 19mm long.

Most of the time, when a special caliber round has a secondary number, it’s because there are other caliber rounds that share its diameter. In the case of 9mm luger, 9mm Makarov also exists, which is 9x18mm, and 9mm Kurz, which is actually 9x17mm. In the United States, we call 9x17mm .380 Auto to help distinguish it from 9mm parabellum.

As far as what these calibers mean in a practical sense, it’s not very straightforward. A larger caliber doesn’t always mean a more powerful round. For example, .45 ACP has considerably less ballistic energy than .357 Magnum despite firing a larger, heavier projectile. This is because kinetic energy is determined by a combination of weight and velocity. That’s why 5.56mm rounds can do so much damage to soft targets despite only firing a 22-caliber bullet. Because that tiny bullet is screaming out of the barrel at upwards of 3,000 fps!

Every year, the NSSF, or National Sports Shooting Foundation, releases sales data that it collects based on NICS checks. They don’t track ammunition sales, but if we extrapolate the calibers of the most prolific handguns, we can get a pretty good idea of what calibers are the most popular. Based on this data, the most popular handgun calibers in the United States are .22lr, 9mm luger, .45 Auto, .38 special/.357 Magnum, and surprisingly, 5.7mm.

What are these calibers, what are they best used for and what do their calibers mean? Let’s examine them one by one and find out.

.22lr, or 22 long rifle, is arguably the single most prolific caliber bullet in the United States by a huge margin. Inexpensive, light-kicking, and plentiful, hundreds of pistols and rifles are chambered in this rimfire cartridge. 

Developed back in 1887, the diminutive little round’s popularity shows no signs of slowing down. While primarily used today for hunting small game and practicing fundamental shooting skills on a budget, .22lr can be found anywhere guns or ammunition are sold.

Unlike the other handgun cartridges on this list, the .22lr is a rimfire round. Meaning that its casing lacks a primer cup. Instead, the base of the round’s case has a priming compound spread around its rim. Hence, rimfire. 

The average .22lr cartridge fires a 40gr lead projectile at around 1,200fps from a rifle-length barrel and 950fps from a handgun barrel. This might seem slow compared to 5.56mm’s 3,000+ fps from a 20-inch barrel, but remember that this translates to roughly 650MPH from a handgun barrel!

It’s this velocity that makes the round such a potent small game cartridge and training aid. The high velocity allows for dramatic hydrostatic shock to soft tissue that, on something like a squirrel, translates into fatal damage. This is especially true when using a hollow-point round that both dumps all that energy into the animal and expands to create a larger wound channel. 

Some people utilize the round for self-defense, but I strongly advise against it. The .22lr’s lightweight projectile doesn’t penetrate thick material well and lacks the terminal energy to cause fight-stopping damage to most human attackers unless a vital area is hit. Not to mention the fact that these rounds tend to be less reliable than centerfire cartridges because the primer compound isn’t always equally spread. This can lead to unreliable detonation, especially on cheaper ammunition.

Regarding training, the .22lr makes a great practice round because it doesn’t have much recoil and has a high enough velocity that it doesn’t have much drop out to 100 yards (at least from a carbine/rifle).

Developed in Austria back in 1901, 9mm parabellum AKA 9x19mm, is the most prolific centerfire cartridge on the planet. While today we think of it as the best all-around handgun in terms of power and capacity, at the time of its inception, it was considered very powerful. Prior to its adoption by the German armed forces, most European militaries issued handguns in much less potent calibers like .32 ACP and .380 Auto. 

Why is 9mm so popular? It’s a combination of cost, controllability, and capacity. Most 9mm handguns are easy to shoot with relatively little felt recoil. Sure, ultra-compact guns can be a little snappy, but compared to .40 S&W or .45 Auto, 9mm is very mild. Especially in the case of the standard 115gr FMJ loading.

It’s also small enough that with the invention of stagger column magazines, most compact and full-sized handguns can hold 15 or more rounds of ammo in a flush-fitting magazine. And based on the FBI crime statistics for armed self-defense, this is plenty for most scenarios. 

Because of these two factors, 9mm ammo became increasingly popular in the United States. This, in turn, leads to greater production and, thus, lower ammo costs. And as the rounds became cheaper, shooters bought more and more of it. We all like to complain about the rising cost of ammunition, but if you look at the purchasing power of the American dollar historically, ammunition is nearly at an all-time low in terms of how much value is spent to acquire it. 

The only thing that held the ammo back for a time was its lack of stopping power and tendency to over-penetrate soft targets. However, with the advent of expanding defensive ammunition, 9mm has become the gold standard for self-defense ammunition. If you’re looking for the cheapest centerfire plinking round that can serve double duty as a defensive tool, 9mm is your ticket.

“Two World Wars!!” Sips sugar-free energy drink while riding a lawn mower.

Yes, the round that saw America through World War 1 and its sequel was developed back in 1904 by John Mosses Browning (Hallowed be thy name!) for his new self-loading pistol, the M1911. The round was developed in response to reports of poor ballistic performance of revolvers used by US troops during the Moro Rebellion in the Philippines.

Big, slow, and heavy, the .45 Auto was a great solution to lackluster stopping power in an era where ballistic science wasn’t advanced enough to produce quality expanding ammunition. If the rounds are over-penetrating, slow them down and make’m heavier!

I’ve often heard shooters refer to the round as the flying ashtray. Heavy enough that it doesn’t have to go extremely fast to inflict damage. The standard load for this 0.45-inch round is a 230gr bullet traveling at around 835 fps. What’s interesting is that most shooters think of .45 ACP as vastly more powerful than 9mm para, but in terms of ballistic energy, the standard 115gr 9mm is only barely less powerful than 230gr FMJ .45 Auto.

That said, defensive +p loadings for .45 ACP can really crank this number to absurd levels, but the two aren’t that far apart. What makes it a better defensive round historically is what I mentioned earlier: it’s larger and traveling slower. So it won’t over-penetrate as often as the higher-velocity 9mm round.

What are the best uses for .45 Auto? For me, it is the king of quiet when it comes to suppressed handguns. That’s because the standard loading for the round is subsonic, so you won’t have to buy more expensive specialty rounds. The other advantage of this is that the round’s efficacy won’t be reduced when suppressed either. 

That sounds great. So why doesn’t everyone carry a .45? Because they’re weak! I’m kidding! The biggest downside of the round stems from what makes it a great defensive round - its size. Because the round is so much larger than 9mm, most.45 Auto handguns have roughly half the magazine capacity of an equivocally-sized 9mm pistol. This, plus the increased mass of the round, tends to produce a more stout recoil impulse, making the gun more difficult to control.

While these rounds are definitely not interchangeable, given that all revolvers chambered in .357 Magnum also fire .38 special, there’s no way to determine which one is more popular based on the NSSF sales figures. Based on my personal experience and talking to dozens of revolver lovers, I’m going to assume the majority of these shooters that bought their revolvers for home or self-defense did so with the intention to run .357 Magnum for defense and .38 special to practice. And if you’re going to buy one, that is exactly what you should do too.

.357 Magnum is a rimmed cartridge measuring 0.357in by 1.59 inches, and on average, propels a 158gr projectile at 1,240fps. This combination produces some serious energy and stopping power. It’s why, when fired from a longer barrel, .357 Magnum can be used to hunt both wild hogs and whitetail deer at close range.

As a defensive cartridge, it will over-penetrate most attackers unless a quality expanding projectile is used. It was developed back in 1934 as an alternative to Colt’s .38 Super cartridge. That round was designed to defeat early bullet-proof vests and automobile doors. .357 Magnum is a stout cartridge that, despite having an identical caliber to the .38 special, is substantially more powerful. 

In my opinion, the .357 Magnum shines as an outdoorsman’s round. Providing ample protection from wolves, small bears, and wild hogs that could become aggressive to a hunter or hiker. Many shooters like to employ snub-nosed revolvers chambered in the round, but I would advise against this unless you’re a recoil junky or an experienced shooter. This combination produces incredible felt recoil with arguably sub-par terminal ballistics as these guns don’t have enough barrel length to fully take advantage of the cartridge’s power.

The 5.7x28mm cartridge was originally designed in 1990 to meet a new NATO request for a personal defense weapon cartridge that would have superior terminal ballistics to 9mm against armored targets. This same request also stipulated that the new round has superior range and accuracy over 9mm luger. The end result was a bottlenecked 5.7mm caliber round that produced rifle-like velocities from pistol-length barrels.

NATO wanted a round that could be used in both traditional handguns as well as select-fire submachine guns. The round that Fabrique Nationale came up with accomplished all these goals in the only realistic way possible: making a high-velocity, small-diameter round with a hardened penetrator. One additional benefit of this round was its incredibly light felt recoil as a result of using such a lightweight projectile.

Indeed, the average 5.7mm projectile weighs a scant 23gr and achieves 2,350 fps when fired from a 10.5in barrel. In many ways, the 5.7mm takes the proven concepts of America’s 5.56mm rifle round and applies them to a pistol cartridge. Namely, a lightweight, high-velocity round that permits impressive magazine capacities in standard mags.

The round always had a cult following in the United States, but it wasn’t until a few years ago, when Ruger introduced their 5.7mm handgun, that the round’s civilian popularity seemingly exploded. As far as why, it’s tough to say. But I can speculate that it stems from the fact that many shooters prescribe to the advantages of a flat-shooting round with remarkably light felt recoil that is so small that standard-sized handguns can hold 20+ rounds of ammunition in a flush-fitting magazine.