I know I promised this post ages ago . . . sorry it took so long!
(Edited to add the pictures, which I forgot the first time.)
Okay, so. Caliber!
From movies, we all hear things like “nine millimeter” and “a thirty-eight.” What does it all mean?
In simplest terms, “caliber” refers to the width of the ammunition round. Ammunition is commonly measured in both millimeters and decimal measures of inches, so a “nine millimeter” is nine millimeters in diameter, and a thirty-eight is (theoretically) .38 inches in diameter (and would usually be written “.38” and pronounced “thirty-eight”).
Sometimes, particularly for rifle ammo, there will be a second number. For instance, 7.62×39 (“seven-six-two by thirty-nine”), the type of round fired by AK-47’s, is 7.62mm wide and 39mm long. The “caliber” is only the 7.62 part, though—saying “7.62x39mm” is actually the cartridge name, since it specifies more than diameter (for example, 7.62x54mmR is a different cartridge from 7.62×39, but is also 7.62 caliber).
That’s the easy part of caliber. Where most writers go wrong is not knowing how these relate to each other.
For instance, 9mm Luger, .38 Special, and .357 Magnum ammunition all have the same diameter (about .36 inches). In general, ammunition of the same diameter is not interchangeable—there are other subtle differences, and guns are chambered for a specific type of ammunition—but the most common exception to this is that you can fire .38 Special out of a .357 (though not the other way around).
Why am I making a point of this? Because I’ve seen TV show characters find a .357 revolver and say, “It can’t be the weapon; the murder was committed with a .38!” when it’s very common to fire .38 Special out of a .357. I’ve also seen TV characters look at a bullet hole and know it’s a .38 instead of a nine-millimeter, which I find . . . unlikely, since the width of the bullet is pretty much exactly the same.
I’ve also seen people assume a wound from, say, a 9mm comes from a handgun. Not true—for instance, MP-5’s fire 9mm. So do Uzis. And not even a different 9mm from most handguns! (There are several types of 9mm, further complicating things if you want to say “nine-millimeter” . . . for instance, the Makarov fires 9×18 ammunition, which is one millimeter shorter than 9mm Luger at 9×19. But 9mm Luger is the most common variant of 9mm by far.)
And this is just the tip of the iceberg. If you want to get into the nitty-gritty of all different ammunition types ever, it’s a mess. Cartridges have evolved from each other over history and spread into a massive variety; different countries have come up with their own types of ammo; some cartridges have used casings inherited from others; old weapons end up re-chambered for modern ammo . . . it reminds me of language, the way cartridges have grown and crossed borders and evolved in a historical tree that’s almost impossible to follow. I don’t know even a thimble-full of all the cartridge types in the world, and I do this for a living.
So for this post, I’m going to talk about some common ammunition types, common mistakes, and what types of weapons they’d be used in. As always, this is the basics only, but most writers won’t need too much more.
Common Handgun Cartridges
To start off with, here are a bunch of common handgun cartridges:
.22 LR: “.22 caliber” usually means .22 Long Rifle (often abbreviated .22 LR if not just .22) if the full name isn’t specified. A lot of people make fun of .22’s as being little more than BB’s; however, they are definitely still very deadly. Firearms chambered in .22 are also the only firearms that can be effectively silenced by a suppressor, which makes it a good caliber for your assassin characters to carry. Despite the name, both handguns and rifles are very commonly chambered in .22 LR. The rounds are very small and very light, and are also the only common rimfire cartridge (for anyone who’s interested in such trivia).
9x19mm Parabellum: “Nine-millimeter” usually refers to 9×19 Parabellum (also called 9mm Luger) if you don’t specify otherwise. Nine-millimeter is a very common caliber for semiautomatic handguns, but as mentioned above is also used in MP-5’s, Uzis, Skorpions, MAC-10’s, and all manner of other more threatening firearms.
.38 Special: An extremely common revolver caliber. Essentially the same as 9mm in terms of size and stopping power, but the two have other differences and are not interchangeable in firearms.
.357 Magnum: Nobody’s sure which handgun ammunition has the fabled “best stopping power,” but .357 Magnum is at the top of the list. Revolvers chambered for this pack a punch. However, almost everyone I know who carries a .357 actually carries it loaded with .38 Special ammo, which is the same diameter but has less powder load. (.357 Magnum rounds are longer than .38 Special rounds, not because they need to be, but so that they won’t fit into a revolver chambered in .38 Special. I’m told the results would be very bad if you tried to fire a .357 Magnum round out of a .38 Special revolver, because .38 Special revolvers are not built to withstand the punch of a more powerful round.)
.40 S&W: Forty is kind of the odd caliber out. I don’t know many people who like firing .40, but that might be because of anecdotal sample size, as clearly someone likes it. It’s quite common for semiautomatic handguns to have both 9mm and .40 caliber variants.
.44 Magnum: Usually a revolver caliber, and a massive one. If you want a revolver that packs a heck of a lot of power, go for a .44 Magnum. This ammunition is most common in revolvers, but other firearms use it as well.
.45 ACP: Usually what people mean by “.45.” Most commonly a semiautomatic handgun caliber, particularly famous for being the ammunition of the M1911. Not exclusive to handguns, however—Tommy guns are chambered in .45 ACP, for instance, as is the new KRISS Vector.
Summary of Common Handgun Calibers: The most common handgun calibers are .22, 9mm, .40, and .45 (in semiautomatics) and .38, .357, and .44 (in revolvers). And by the way, if you’re tempted to give your character a .50-caliber handgun, please don’t. It’s ridiculous.
Now for a picture:
Common Rifle Cartridges
Rifle cartridges are in general (but not always) larger and more dangerous-looking than handgun cartridges. Take a look at the two rifle cartridges on the left of this picture, compared to a row of handgun cartridges:
Here are some common rifle cartridges:
.22 LR: See above. There are a ton of rifles chambered in .22 LR. They are by and large considered “plinkers,” but are fun weapons. When kids fire rifles in Scouts I’d assume them to be .22’s.
7.62x51mm (military) / .308 Winchester (civilian): Most of my friends who are dedicated rifle shooters are a fan of the .308 (“three-oh-eight”). It’s a solid round that doesn’t go overboard. The M14 rifle and the M60 machine gun use this type of ammunition.
7.62x54mmR: Pronounced “seven-six-two by fifty-four R.” A round in very widespread use, most notably in the very popular Mosin-Nagant rifle. The Dragonuv sniper rifle also uses this round.
7.62x39mm: Pronounced “seven-six-two by thirty-nine.” The ammunition for the AK-47, the SKS, and the RPD. Considering the popularity of the AK-47, this cartridge is in very widespread use. Without any other context, I would assume someone saying “7.62” meant this cartridge.
5.56x45mm NATO (military) / .223 Remington (civilian): Pronounced “five-five-six” / “two-two-three.” A standard U.S. military cartridge. Used in M4’s and M16’s.
.30-06 Springfield: Pronounced “thirty-aught-six.” A .30-06 is very powerful. It will blast a target apart.
.30-30 Winchester: Pronounced “thirty-thirty.” Popular in hunting, I believe. Lever-action rifles are commonly chambered for this.
.50 BMG: Okay, maybe this isn’t exactly common, but we’re talking about fiction, right? Bigger is better! Seriously, a .50 caliber will go through anything. It will bust through layers of concrete. It disintegrates. If your character’s arm is grazed by a .50 cal, that arm becomes pink mist. (So I’m told.) These things are powerful.
Again, this isn’t a complete list, but I think I’ve covered most of the common ones. For rifles, I think you’d be better off choosing your firearm and then looking up what it’s chambered in.
Here’s a picture comparing different common rifle cartridges:
“But wait!” I hear you cry. “What about shotguns?”
Well, shotgun ammunition isn’t usually designated by caliber (except for .410 shotgun ammo, just to make things extra confusing). Instead, we measure it by gauge.
How does gauge work? Well, it’s an archaic measurement using lead balls and weight. A 12-gauge shotgun has a bore diameter equal to that of a ball of lead weighing 1/12 pound. A 16-gauge shotgun has a bore diameter equal to that of a ball of lead weight 1/16 pound.
As a writer, you probably don’t need to know that. Just know that a larger gauge = smaller ammo. So 12-gauge is bigger than 16-gauge which is bigger than 20-gauge.
By far, the most common ammunition for a shotgun is 12-gauge. By far. If you’re doing something other than 12-gauge, you should probably have a reason. Other than that, the only other types of shotguns I’ve even seen are chambered in 16-gauge or 20-gauge (or .410, which is titchy). Here’s a photo comparison of some different shotgun gauges:
In general, if you want a shotgun, just use a 12-gauge.
And incidentally, because 12-gauge is the most common, it would be weird for your characters to be surprised or to make note of a shotgun being 12-gauge.
Okay! I hope this was helpful! As always, feel free to ask questions in the comments. And here’s the rest of the “Gun Basics for Writers” series so far!
- I guess I should mention the .500 Smith & Wesson Magnum. It’s a revolver cartridge. Seriously. A .50-caliber handgun. The thing is a freakin’ hand cannon. I’ve seen it break experienced shooters’ wrists when they fired it too many times in a row. Nobody uses the things, at least not for self-defense or carry weapons.↵