Handgun Calibers – The Definitive Guide

handgun caliber guide

If you’re a new shooter, deciding what caliber to use can be a difficult affair. However, there’s more to ammunition than caliber. In this article, we’re going to explain exactly what caliber is and take a look at some of the most popular handgun cartridges on the market today. We will also explain some pros and cons of each cartridge, so you can make an informed decision on what will work best for you.

Basic Terminology

For the newest shooters, deciphering all the numbers and letters on the ammo boxes at the local sporting goods store can feel like reading a foreign language. A basic understanding of common ammo terms will help you decode all that info on the packaging. Here are the definitions of some of the most basic and important terms. 


We’ll start with caliber, since that’s the term that probably landed you on this page. Simply put, caliber is the diameter of a bullet measured in inches. 

Sometimes bullet diameter is expressed in metric measurements (think millimeters) rather than imperial inches. In the strictest sense of the word, metric measurements aren’t “Caliber.” However, modern shooters use the word to simply describe the diameter of a bullet (or the diameter of the bore if you’re talking about a firearm instead of ammunition). 

If diameter is expressed in millimeters, we drop the word caliber after the designation. In gun circles, you wouldn’t use the term “9mm caliber” unless you want to get some serious side eye. Instead, just call it “nine millimeter”. 

Keep the term caliber when the diameter is expressed in inches (but don’t pronounce the decimal). For example, .40 would be referred to as “forty caliber”. Sometimes manufacturers leave the decimal out entirely. However, the decimal is implied even if it isn’t there. 


Bullet weight is measured in grains. Often shortened to “gr”, a grain equals 1/7,000 of a pound. In other words, there are 7,000 grains in one pound. One ounce is equal to 437.5 grains.


FMJ is an acronym for “full metal jacket”. This is a projectile design that features a soft lead core encased in a harder (usually copper) metal. FMJ loads are most commonly used for target shooting and tactical training.

Hollow Points

Often shortened to “HP”, a hollow point is a specific projectile design. These bullets are hollowed out at the tip. When the bullet strikes a soft target, pressure builds in the cavity, forcing the walls around the hollow pit to expand outward. The expansion increases the diameter of the bullet as well as the wound channel it carves through the target. Hollow points are usually used for hunting and self-defense applications.  


Sometimes the term “caliber” is used when referring to “cartridges”. However, the two words have different meanings and aren’t really interchangeable. 

While caliber refers to bullet diameter, the word “cartridge” refers to the whole kit and caboodle. A cartridge is one round of ammunition and includes the case, primer, powder, and the bullet. 

There are often multiple cartridge designs that use the same caliber bullet. For example, .38 Short Colt, .38 Long Colt, .38 Special (and even .357 Magnum) all use the same caliber bullets. However, the case dimensions and powder charges differ. Since they are not interchangeable (with few exceptions), it is important to know the difference. 

Common Handgun Cartridges (and their Caliber)

.22 Long Rifle

22 long rifle ammo

The twenty-two long rifle (abbreviated to .22 LR) is a common rimfire cartridge. This means the primer is located around the rim of the case rather than in the center (which is where the primer is located for centerfire cartridges). 

.22LR cartridges fire relatively small .22 caliber bullets. Just don’t let the paltry size fool you. The .22 LR is still a deadly round. Even though they are generally considered ineffective for self-defense and big game hunting, a .22 caliber round to the right spot can have lethal results. .22 rounds are also known to tumble in soft tissue, which can cause serious internal damage.

Since .22 LR produces ultra-mild recoil, it is often used to introduce youngsters to shooting. Many serious adult shooters fired their first shots through a .22 LR pistol or rifle when they were only children. 

The .22 LR is great for beginners. Because it is so easy to shoot, .22 LR is often used for plinking and recreational target shooting. However, the .22 LR is no stranger to the competition field and is a common round for hunting varmints and small game. 

.380 ACP

best 380 ammo

Officially known as the .380 ACP (Automatic Colt Pistol), this cartridge is sometimes called 9mm Short or 9mm Kurtz. Although this cartridge uses the same diameter projectile as the popular 9mm Parabellum, the .380 ACP uses a much shorter case length (.680 inches compared to the .754 inches used in 9mm Parabellum).

Because .380 ACP cartridges hold less powder, they are far less powerful than standard 9mm. However, these cartridges are a popular chambering for small pocket pistols. 

Don’t confuse .380 ACP (.380 Auto) with .38 ACP (.38 Auto). They are two very different cartridges and are not interchangeable. 

9mm Parabellum

best 9mm ammo

The 9mm Parabellum is also called 9x19mm, 9mm Luger and 9mm NATO, although it is most often referred to as simply “nine millimeter.” 

The 9mm produces mild recoil while delivering highly effective terminal ballistics (especially with cutting-edge self-defense ammo). Even full-size 9mm handguns are generally light enough for EDC (every day carry) while providing a generous magazine capacity. 

More than 60 percent of law enforcement agencies (including the FBI) use 9mm Parabellum in their duty weapons. Even U.S. Navy SEALS carry 9mm sidearms. The cartridge is also incredibly popular for civilian concealed carry and home defense

There is a plethora of 9mm ammo to choose from. There are variations optimized for law enforcement, self-defense, and target shooting. 9mm is also relatively affordable and readily available from most ammo retailers. 

.38 Smith & Wesson Special

best 38 special ammo

Until the 1990s, most law enforcement officers carried revolvers chambered in .38 Special (sometimes shortened to .38 SPL). While few police units still issue .38 SPL duty weapons, the cartridge is still used by many off-duty or undercover officers in some short barrel, snub nose revolvers.

A .38 SPL revolver (especially a snubbie) is generally easy to conceal and makes a solid back-up weapon.  

.357 Smith & Wesson Magnum 

best 357 ammo

Despite the number differences, the design of the .357 Magnum cartridge (also known as .353 Casull and 9x33mmR) was based on the .38 SPL. Both cartridges use projectiles that measure .357 inches in diameter.

The .357 Magnum was developed specifically for law enforcement during the American “Gangster Era” that followed World War I. Police officers needed a cartridge capable of penetrating thick steel car bodies and the early ballistic vests often used by the professional bank robbers of the day. To achieve the goal, ammo manufacturer Smith & Wesson lengthened the .38 Special case by ⅛ of an inch and loaded the cartridge to produce higher pressures. 

The original .357 Magnum design featured a bullet with a large, flat nose. With higher pressures and a non-deforming bullet, the .357 Magnum accomplished effective penetration, even on tough shooting targets. The original design also makes the .357 Magnum a great choice for hunting and target shooting. 

Modern shooters can find .357 Magnum ammunition made with almost every bullet style under the sun, including hollow points, FMJs, and traditional flat nose (FN) bullets. 

Handguns chambered in .357 Magnum can also safely shoot .38 Special cartridges. However, the reverse is not true. 

.40 Smith & Wesson

best 40 s&w ammo

In the early 1990s, the .40 S&W became the standard issue duty gun for law enforcement organizations across the country. However, the .40 S&W is rapidly losing favor in the law enforcement sphere and has been mostly replaced by 9mm Parabellum. 

The .40 S&W cartridge is basically a shortened version of the 10mm Auto. Like the 10mm, the .40 S&W fires a .40 caliber projectile. However, it fires that projectile at a reduced velocity compared to standard 10mm.  

.40 S&W is known to produce some pretty snappy recoil, which can be difficult for some shooters to control. This cartridge is most commonly used for personal protection. However, it is also sometimes used for hunting and target competition.

10mm Auto

best 10mm ammo

First introduced in 1983, the 10mm Auto cartridge was developed by the legendary Jeff Cooper (who also fathered the Modern Technique of the Pistol and penned The Four Basic Rules for Gun Safety). Originally called the .40 Super, this cartridge was designed to produce flatter trajectories and provide a longer effective range than the .45 ACP, while delivering more terminal energy transfer than 9mm. 

The case of Cooper’s 10mm Auto was derived from the .30 Remington rifle cartridge, with the case cut down and straightened to accept a hefty .40 caliber bullet. 

Although .40 S&W and 10mm cartridges both fire .40-caliber rounds, the projectiles used in 10mm ammo are usually longer and heavier than the bullets used in .40 S&W. With a longer case, 10mm Auto also holds more powder. As a result, 10mm produces significantly faster velocities than .40 S&W loads.

It takes a lot of power to push those heavy projectiles downrange at such impressive speeds. It should come as no surprise that 10mm Auto produces some pretty heinous recoil. This isn’t a cartridge you want to use for a long day of casual, recreational plinking.

Although the 10mm Auto has had some law enforcement use, it has been mostly abandoned due to its excessive recoil.

The 10mm Auto is one of the few rimless semi-auto cartridges that can be legally used to hunt whitetails in almost all 50 states. The cartridge is also a favorite for hunters pursuing large and dangerous game. 

.44 Remington Magnum

44 Remington Magnum

The .44 Remington Magnum is more commonly called “44 Magnum.” The cartridge is based on the .44 Special case, only longer and loaded for increased pressure and faster velocities. 

Designed in the 1950s, the .44 Magnum is a dual-purpose cartridge that can be used in both handguns and rifles. A popular choice for handgun hunters, .44 Magnum is perfectly capable of dropping elk-size game. The cartridge was even used by American publisher, Robert E. Petersen, to harvest a 1500-pound polar bear with his Smith & Wesson Model 29 revolver. 

The .44 Magnum gained major popularity after its appearance in the Dirty Harry films. However, .44 Magnum handguns make pretty beastly duty weapons. As such, they are mostly used for hunting. 

.45 ACP

45 acp ammo

The .45 ACP (sometimes called .45 Automatic Colt Pistol or .45 Auto) was designed by the legendary John Moses Browning. The cartridge is most often associated with Browning’s iconic Colt Model 1911. Read out article about 1911 holster options here.

The Colt 1911, along with the .45 ACP cartridge, served US military troops through two world wars, Korea, Vietnam, and most of the Cold War. It was eventually replaced by the Beretta M9 (which is chambered for 9mm Parabellum) in 1985. However, .45 ACP is still widely used by America’s elite fighting soldiers. It also remains a popular choice for civilian home and personal defense. 

The .45 ACP fires large, heavy bullets at fairly fast velocities, which results in some solid recoil. However, since most .45 pistols are also pretty hefty, much of the recoil is absorbed by the weapon. Many shooters actually claim the recoil produced by .40 S&W is more intense than the recoil produced by the larger .45 ACP. 

The .45 ACP is an adequate hunting round. However, they are more appropriate for small to medium game and varmints. Save the elk for the .44 Magnum. 

Wrapping It Up

Whether you’re gearing up for serious competition, self-defense, hunting, or target shooting, the handgun caliber and cartridge you choose, when combined with the right handgun scope or red dot can make or break your shooting experience. While we have included the most popular handgun cartridges, this is by no means an exhaustive list. There are literally hundreds of other handgun cartridges in production today.

We’ve tried to cover all of the basics. However, the information in this article is definitely simplified. This was necessary for reasons of space as well as to keep things uncomplicated for readers new to handguns and ammunition. Consider this simply an introduction. If you want to know more, be sure to check out our in-depth ammo reviews.

Photo of author

Alice Jones Webb

Alice Jones Webb is a writer, life-long hunter, experienced shooter, and mother of 4 up-and-coming shooting and outdoor enthusiasts. She grew up flinging arrows and bullets at Virginia whitetails, turkey, and game birds, but her favorite hunting experience is chasing bull elk in the Colorado backcountry. Never one to sit still and look pretty, Alice is also a self-defense instructor and competitive archer. She currently resides in rural North Carolina with her children, non-hunting husband, and a well-stocked chest freezer.

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