A Helpful Guide to Guns in Fiction, Part 2

Calibers and Gauges

Even if you are not very familiar with firearms, you might be required or want to write about them. But there is a lot of terminology and it can be very confusing. This is especially true of cartridge calibers and shell sizes. A popular choice for clueless writers is to simply assume that higher numbers means more dangerous or to just use rounds that they have heard about in other sources without understanding what they are talking about. Here are some helpful things to know-

1. They are called cartridges or rounds, not bullets, until they've been fired. In fiction, people usually use the term bullet when they mean cartridge. The bullet is the projectile part that is fired from the gun and hits a target. The cartridge is the bullet seated in a brass casing that is loaded with powder with a small high explosive at the back of the casing that is detonated by the firing pin. The small high explosive is called a primer. The casing is the part that is ejected from the gun, usually up and to the right, or is emptied out before the gun is reloaded.
2. Shotguns use shells. This is because most shotguns do not fire a single projectile, but several smaller projectiles that spread (a small amount, not the huge spread popular in movies) when they are fired. A shell contains a metal back piece with the primer. This is connected to a plastic or paper tube (frequently green or red). The tube is filled with powder in the back and a group of metal balls backed into a small bag in the front. Usually a plug separates the two, it is called a wad.
3. The number in a cartridge's name is called the caliber. It can be misleading. It does not mean anything about the rounds power and some numbers can sound higher "so they must be better right" but are actually higher? The caliber is actually just a measure of the bullet's diameter. It is either in English units or Metric. When in English units it will usually be written with a period than a number. This is the diameter's measurement in inches. For example, a .22 Long Rifle, is 0.22 inches in diameter. A .45 ACP is 0.45 inches in diameter. Metric measurements will be given in millimeters, such as the 9 mm Parabellum. They are also sometimes called by the caliber of the bullet and the length of the whole cartridge. For example, 7.62x39mm.
3.1 When the name is said though, the decimal is not said and the second part of the bullet name may be dropped. So those two rounds would be said "22 Long Rifle or just 22" and "45 ACP or just 45". This convention of just saying the caliber can be confusing when multiple different cartridges of the same size are made. For example the .45 Colt and .45 ACP.
3.2 Just because three numbers are given does not mean that the bullet is larger. For example, a .223 Remington has a smaller diameter than a .45 Colt, even though the the first is said "223" and the second is said "45".
3.3 The naming conventions have not always been consistent, sometimes it was the size of the cartridge and sometimes the size of the casing, which might be slightly larger. For example, the .38 Special and .357 magnum are the same size for this reason. The first is based upon the case size and the second on the bullet size.
3.4 A helpful point of reference between metric and English is the 9mm Parabellum and the .357 magnum. The 9mm and the .357 magnum are very close to the same diameter. They are however, very different cartridges.
3.5 Some rounds have multiple names. Most commonly military rounds that are also produced for civilians firearms or cartridges made in different places. The most common is probably the NATO 5.56 mm and the .223 Remington, with are variants of the military and civilian variants of the same cartridge.
3.6 The term magnum implies that the round is a more powerful cartridge than other cartridges of the same size. This is not always true, but is a good guideline.
4. The size of the bullet will give some indication of how big a hole it will make and therefore how dangerous it will be, but it is not the only or necessarily the most important factor. The M-16 fires a 5.56 mm (or .223 Remington) that is in many ways more dangerous than a .38 Special, which is much larger. Other factors are the speed at which the bullet travels, the shape of the tip, the weight of the bullet, and the stability of the bullet. Bullets work by transferring energy and momentum to a target. Some bullets, such as the 5.56 mm, do this by starting to tumble to create a bigger wound than the caliber would indicate.
5. Shotguns use gauges rather than calibers. This has a very counterintuitive naming system. The Smaller the Gauge, the larger the shotgun barrel. This comes from an old way of measuring barrels and represents the number of solid lead spheres of the same diameter as the barrel that can be made from a pound of lead. Therefore, a 12 gauge is larger than a 20 gauge (the two common shotgun gauges). For reference, a 12 gauge is .729 caliber and a 20 gauge is .665 caliber.
6. There is usually a distinction made between pistol ammo and rifle ammo. Though the two overlap some and cartridges originally designed for one type of weapon might be used in another.
Generally, pistol ammo will be smaller and have relatively straight cylinder shaped casings. Pistol ammo is used by submachine guns, such as Uzi's or Tommy Guns.
Rifle ammo tends to be much longer and larger. It is very common for rifle cartridges to have tapered sides and to have a bottleneck near the bullet. They are usually used in assault rifles, hunting rifles, sniper rifles and in larger machine guns.
7. Two types of common bullets are used for handguns (there are probably more variants then I can think of, but I'm only covering these two). Full Metal Jackets (FMJ) and Jacketed Hollow Points (JHP), sometimes just called Hollow Points. FMJs are a lead bullet with a metal jacket (usually of a copper-nickel alloy). The metal jacket prevents damage to the barrel or lead build up. They make a hole of about their own size. JHP have a recess in the front of the bullet. They are designed to catch in a target then expand outward in a mushroom shape so that they cause more damage. JHP are not frequently used for military purposes, but are popular among police forces because they are less likely to overpenetrate (go through the person being shot and hit something or someone behind them).
8. Shotguns fire two different types of ammo regularly, shot and slugs. Shot is small pellets. Bird shot is very small circular pellets, typically 1/6" or less. These are not designed to penetrate large targets and will generally only go 1-3 inches into a person. A shot from birdshot is very survivable. Buckshot is larger circular pellets, typically 1/4" or greater. (double ought is 1/3" for those that are curious) It tends to be much more deadly than birdshot. Slugs are solid lead projectiles that replace the packed pellets in a normal round. They tend to be less accurate at long ranges, but because they are heavy and large in diameter can be very dangerous. They are designed for hunting large game.

Hope that makes some sense of calibers for you. Below is a list of some common cartridges ranked by the amount of energy they typically deliver from lowest to highest. (Energy does not necessarily mean how deadly they are, but it does give some idea and also gives an indication of how much penetration potential they have)

Pistol Rounds
1. .22 Long Rifle (popular for small game and target shooting)
2. .38 special (a lot of old style police revolvers fire these)
3. 9 mm Parabellum (Glocks and Berettas are frequently chambered in 9mm)
4. .45 Colt (A popular revolver round coming down from the Colt Single Action Army revolver of the 1800's. Modern loadings are more powerful)
5. .45 ACP (Automatic Colt Pistol, used by Tommy guns and 1911s)
6. .357 magnum (a more powerful replacement for the .38 special)
7. .44 magnum (Dirty Harry's weapon of choice)

Rifle Rounds
1. .223 Remington (5.56 mm) (The M-16's round)
2. 7.62x39mm (The AK-47's round)
3. .308 Winchester (7.62x51mm NATO) (Used by the M-14 and is popular for police sniper rifles and hunters.
4. .30-06 Springfield (Here the 06 designates 1906. This is the round used by Springfield M1906, during World War I, and used in the M1 Garand in World War II)
5. .300 Win Mag (A more powerful rifle round for hunting large game like bears)
6. .50 BMG (Also called a 50 Cal. It is designed for penetrating engine blocks and damage other material targets, to be fired by heavy machine guns. It is also frequently used by snipers)