Calibers: What They Say About a Gun

Let's get it straight to begin with: The caliber is just the inside diameter of a revolver, a semi-automatic pistol or a rifle barrel and contrary to what a large number of people believe, it's not the size of the gun or a representation of the speed of the bullet. The caliber also determines the designation of the ammo used in a particular gun and there's intricate physics that comes into play; however, we are here just to clear the confusions on the bores/calibers and the different kinds of ammunitions and not to design the 21st century wonder-machine. We'll stick to the basics.

Since caliber is just the diameter of a gun barrel, it also represents the projectile's (bullet's) size. It is another vital factor that classifies the firearms. A caliber is expressed either in millimeters or in decimal points/fractions of an inch. The mm is a European practice, whereas the decimal system is purely American.

Thus, when you speak about a .22 caliber firearm, you can be sure of it being of a diameter that's twenty-two hundredths of an inch. Knowing this much only shall help you not to be eluded by the paperback detective novels, unless you deliberately find the decimal point an impenetrable mystery and prefer sticking to such ludicrous firearm descriptions as a .9mm Walther. As far as I know, no bullet has ever been developed with a diameter of only 9/10ths of a millimeter; none can inflict even a moderately grievous wound with something about the size of the point of an average-sized needle.

Now, a little more on the representation. Let's take a very popular example: the Walther PPK used by James Bond. It is a 7.65mm caliber semi-automatic pistol (not a revolver) but in the US, the same caliber shall be represented as a .32 automatic. If you still find it a baffling affair, try converting .32 inches into millimeters and you shall find an answer. And when representing a caliber in mm, it is heresy to add the word caliber as a suffix. You can add caliber with the decimal system (e.g. a .45 caliber revolver which is as good as mentioning a .45 revolver) but not after you mention 9mm or 7.65mm. However, military weapons have made the metric designation an universal affair; this makes a 9mm. pistol or its cartridge to get recognized both in Europe and the US, especially if it's a common 9mm. Parabellum (formerly known as Luger). For representing the less powerful 9mm. Short/Corto/Kurz, in the US, it's the .38; in Europe, a .380. This is because Europeans prefer expressing calibers in three digits if they go the decimal way, one of the examples of English complications.

But here comes the real blow: An official designation of caliber by a firearm manufacturer may or may not reflect accurately the actual inner-barrel dimension. The metric designations are easy to deal with if rounded up to the closest value of an actual measurement; this is why a .38 Special bullet and a .357 Magnum bullet can be chambered in a .38 caliber revolver (but not the other way round). Both the types have the same diameter; it's the heavier powder charge in a somewhat longer case that differentiates the Magnum from the Special. However, for .38 S&W, it's the weight of the projectile (200 grains) that makes the difference. It's represented as a .38/200. And oh, never be fooled by someone who adds the decimal while narrating the caliber of shotguns, which are classified in gauge and are inversely proportional to the given number. This makes a 12-gauge shotgun (not a .12 gauge) is bigger and more powerful than a 20-gauge; therefore, if anyone challenges you to beat down with his 20-gauge your 12 gauge one, warn him that he is in for some very hard time.