One of the least understood topics for pistols is what caliber really means. As a result, we made a handgun caliber comparison chart, and guide that faces this issue head-on.
At its most basic definition for guns, caliber refers to the diameter of the inner opening (aka bore) of a gun barrel. Likewise, caliber also refers to the diameter of a bullet. These measurements are typically expressed in fractions of an inch.
A common misconception is that a bullet is one unit of ammunition. However, bullets are only the metal projectile that is ejected from the gun when fired. One unit of ammunition is called a cartridge.
Let's look at two common examples:
Simple stuff once you think about it.
Now, let us focus on the bullet itself, and compare some of the most common pistol calibers. We will be comparing the following key parameters for each caliber:
Note: Before we dive in, let us explain that we will be avoiding the classic pistol caliber debate in this guide. Instead we are presenting the information to allow you to make your own conclusions. Now the fun part....
.22 calibers are notable as being one of the last remaining commonly-manufactured type of rimfire ammunition, i.e. rounds wherein the powder is set aflame by primer located in the rim of the cartridge. Most common pistol calibers today are "center-fire," with the primer located on a striking surface at the center of the casing instead. The .22 rounds themselves differ only in terms of length and powder charge; all fire a small, light projectile. As a result, the .22 is most suited for target practice and small game hunting. The .22 has acquired a folkloric reputation for lethality due to its supposed propensity to bounce around inside a target. However, this has been widely disconfirmed by modern studies of stopping power.
Twenty-five and thirty-two, the "sub-combat" calibers, occupy a strange space in the world of mainstream handgun ammunition. Both offer a light, short cartridge suitable for an easily-concealed handgun, but neither offer particularly impressive ballistics. In fact, both are widely regarded in defensive handgun circles as being too underpowered for self-defense or hunting and too expensive for those multi-thousand-round days at the plinking range. Originally developed during the era of nascent semi-automatic pistols, both rounds were intended for self-defense but have since been supplanted by superior alternatives which offer more mass, velocity, or both. Consequently, outside of collectors' firearms and backup guns, neither cartridge is commonly recommended for everyday use.
As similar as their caliber is, these rounds could not be more different. Both occupy the medium-diameter category at just under four-tenths of an inch. However, these rounds were designed with different roles in mind. .380 ACP makes up the smallest of the combat calibers with a moderate-diameter bullet and a small charge of powder designed for controllable recoil in small-frame automatics. .38 Special, by contrast, predominantly feeds revolvers due to its significantly larger powder charge and therefore higher muzzle energy.
As their name implies, both of these rounds are quite large and, due to the high muzzle velocities they produce, exceptionally powerful. The smaller of the two, .357, became one of America's most popular self-defense calibers when it was retooled from the existing .38 Special cartridge during the 1930's. The larger .44 came about two decades later, and both remain popular for self-defense applications and, to a limited extent, hunting. Many carbines chambered in these type of ammunition exist, most of which mimic the lever actions of yesteryear modernized for today's ammo. Due to the enormous pressures involved, very few semi-automatic firearms are capable of feeding magnum rounds; an exception is the Israeli Military Industries Desert Eagle pistol, of Hollywood fame. Versions of the Desert Eagle exist chambered in in .357 magnum, .44 magnum, and Action Arms' proprietary .50 Action Express magnum round.
The practice of naming newly-created calibers by their intended firearm continues to this day.
The world's most popular pistol round, the 9x19mm Luger or Parabellum was designed for military and police applications. Militaries and police take advantage of the cartridge's superior ballistic characteristics and relatively light weight. As a result, more than half of US police are issued handguns in this caliber and it remains one of the most popular ammunition types for submachine guns as well. Its secret lies in the high velocity of the relatively small round; while only three-hundredths of an inch wider than a .32 ACP.
A 9x19mm bullet flies much faster and therefore transfers dramatically more energy to the target, resulting in a higher likelihood of stopping the target for each round fired. At the same time, 9mm rounds are light, affordable, and nearly ubiquitous, making them a great choice for regular practice. Overpressured 9mm rounds are a common choice for self-defense, especially in hollowpoint configurations designed to expand on impact.
10 mm Auto
The forty-caliber cartridges, .40 Smith & Wesson and its longer cousin, 10mm Automatic, offer larger, heavier bullets than most pistol cartridges without sacrificing too much in the way of velocity. Originally developed in the 1980's, the 10mm Auto rose to brief prominence after the FBI selected the cartridge to replace their .38 Specials and 9mms. This decision was made in the wake of a disastrous shootout in Miami. During the shootout a bank robber was able to continue killing and wounding FBI agents despite having been struck half a dozen times by their handgun bullets.
The heavy 10mm round and large powder charge proved seriously capable in the right hands, but field testing revealed that the powerful recoil and large size of handguns chambered in 10mm made it difficult for most law enforcement officers to reliably make follow-up shots. A shortened spinoff, the .40 S&W, garnered widespread acclaim and rapidly became one of the most popular defensive handgun calibers. In many senses, .40 S&W straddles the line between the small, high-velocity 9x19mm round and the large, lower-velocity .45 ACP; many varieties exist which allow shooters to select their favorite balance of mass and projectile velocity.
One of the twentieth century's best-known pistol cartridges, the venerable .45 Automatic Colt Pistol cartridge originally supplanted the .38 Long Colt cartridge during the Moro uprisings in the Philippines. (For more information on the history of this venerable cartridge, check out our guide to the best IWB holsters for 1911 pistols!) On the mass-to-velocity index of pistol ammunition, this round goes for mass above all else; its low muzzle velocity is sufficient for penetration but the round relies on its enormous weight for its lethal characteristics. A pistol caliber comparison chart will typically list this as the largest of common self-defense rounds by caliber alone. While it lacks the sheer destructive power of other large rounds such as the .44 Magnum, the .45 ACP allows for much quicker follow-up shots due to its lower recoil and smaller muzzle blast. On the downside, the round's large diameter mean that most handguns chambered for this cartridge hold fewer rounds than their 9mm or .40 S&W equivalent.
To clarify, whether you're equipping yourself for target practice or self-defense, the choice of caliber can make quite a bit of difference. As larger rounds require more material to manufacture and less-common rounds receive less benefit from economies of scale in their manufacturing, common calibers such as 9x19, .40 and .45 tend to dominate the mainstream handgun market. Plinkers gravitate toward the small end of the spectrum, while those needing protection from ornery wildlife commonly rely on magnum cartridges to bring them home safe. Whatever your needs, check out our pistol caliber chart and learn more about your favorite caliber. Once you have purchased the correct caliber pistol, check out our Best IWB Holster Review to find the holster that is right for you. Until next time, stay safe and stay on target!