A cartridge is four parts and a name. The name tells you almost everything, if you know how to read it, and it's what prevents the accident.
What's in a cartridge
The case, usually brass, sometimes lacquered steel or aluminium. It holds everything together, and when fired it expands against the chamber to seal it.
The primer, in the base. A small shock-sensitive charge, struck by the firing pin, that sends a flame into the powder.
The powder, today smokeless, based on nitrocellulose. It doesn't detonate: it burns very fast and makes gas that pushes.
The projectile, the bullet. Bare lead, copper-jacketed lead, solid copper, sometimes with a steel core.
Two big families of priming:
- Rimfire: the priming compound sits in the rim of the base. The firing pin crushes the edge. That's the .22 LR. These cartridges can't be reloaded.
- Centerfire: a round primer in the centre of the base. Almost all the others. The case can be reloaded.
Reading a caliber name
The metric system gives two numbers: bullet diameter, then case length, in millimetres. 9 × 19 mm, 7.62 × 39 mm, 5.56 × 45 mm.
The imperial system gives the diameter in hundredths or thousandths of an inch, followed by a name: .22 Long Rifle, .45 ACP, .308 Winchester.
The same round often has several names. 9 × 19 mm is also called 9 mm Parabellum, 9 mm Luger or 9 mm NATO. The .380 ACP is the 9 × 17 mm, also called 9 mm Short or 9 mm Kurz.
And two different rounds sometimes share a number. The 9 mm Makarov (9 × 18 mm) is not a 9 × 19. The 7.62 × 39 (Kalashnikov) has nothing to do with the 7.62 × 51 (NATO) or the 7.62 × 54R (Mosin-Nagant, Dragunov). Always read the full marking, never just the number.
The marking is stamped on the case base (the headstamp): maker, caliber, sometimes year. On the gun, the caliber is engraved on the barrel or the slide. The two must match exactly.
Common calibers
Typical values, which vary with the load and the barrel length.
| Caliber | Other names | Use | Bullet | Velocity | Energy |
|---|---|---|---|---|---|
| .22 LR | 22 long rifle, 5.6 mm | Target, small game | 2.6 g (40 gr) | 330 m/s | 140 J |
| .380 ACP | 9 × 17, 9 mm Short | Pocket pistol | 6.2 g | 290 m/s | 260 J |
| 9 × 18 Makarov | 9 mm PM | Former Eastern-bloc pistols | 6.1 g | 315 m/s | 300 J |
| 9 × 19 | 9 mm Parabellum, Luger, NATO | Pistol and submachine gun, the most common in the world | 8 g (124 gr) | 360 m/s | 500 J |
| .38 Special | 38 Spl | Revolver | 10.2 g | 270 m/s | 370 J |
| .357 Magnum | 357 Mag | Revolver, also fires .38 Special | 10.2 g | 400 m/s | 800 J |
| .40 S&W | 10 × 22 | Police pistol (United States) | 11.7 g | 330 m/s | 640 J |
| .45 ACP | 11.43 × 23 | Pistol | 15 g (230 gr) | 255 m/s | 490 J |
| 5.56 × 45 NATO | .223 Remington (close) | Western assault rifle | 4 g | 940 m/s | 1,750 J |
| 7.62 × 39 | 7.62 Soviet, M43 | Kalashnikov, SKS | 8 g | 715 m/s | 2,050 J |
| 7.62 × 51 NATO | .308 Winchester (close) | Precision rifle, machine gun, hunting | 9.5 g | 850 m/s | 3,400 J |
| 7.62 × 54R | 7.62 Russian | Mosin-Nagant, Dragunov, PKM | 9.6 g | 830 m/s | 3,300 J |
| .30-06 Springfield | 7.62 × 63 | Hunting, older rifles | 11.7 g | 820 m/s | 3,900 J |
| 12.7 × 99 NATO | .50 BMG | Heavy machine gun, anti-materiel | 42 g | 900 m/s | 17,000 J |
| 12 gauge slug | Shotgun, big game | 28 g | 450 m/s | 2,800 J |
To compare these energies and understand what they do to a target, see La balistique.
The shotgun: caliber backwards
For smoothbore guns, the "gauge" is a number of lead balls: a 12 gauge barrel has the diameter of a lead ball weighing one twelfth of a pound. The bigger the number, the smaller the barrel. A 12 gauge is about 18.5 mm, a 20 gauge about 15.6 mm. The .410 is the exception: it's a true diameter in inches.
Three main loads:
- Birdshot (sizes 6 to 9): birds, small game. It loses its energy within a few dozen metres.
- Buckshot: about ten large pellets. Big game at short range, defence.
- Slug: a single heavy projectile, for big game.
Shell length matters too: 65, 70 or 76 mm (2½, 2¾ or 3 in). A shell too long for the chamber raises pressure dangerously.
Bullet types
- Full metal jacket (FMJ): lead core fully covered in copper. It goes through and deforms little. Standard military round.
- Jacketed hollow point (JHP): a cavity at the front. It opens on impact, transfers its energy, goes through less. Police and defence round.
- Soft point (SP): exposed lead at the front that flattens in a controlled way. The classic hunting round.
- Tracer: a compound in the base burns in flight and shows the trajectory. It can start a fire in dry grass.
- Armour-piercing: hard steel or tungsten core, to go through protection.
- Subsonic: under 340 m/s, so no supersonic crack. Useful with a suppressor.
What can't be swapped
A cartridge is only fired in the gun made for it. The exceptions are known and limited:
- a .357 Magnum revolver fires .38 Special, not the reverse;
- a gun chambered in 5.56 NATO fires .223 Remington; the reverse is not advised, 5.56 runs at higher pressure;
- a gun in 7.62 × 51 generally fires .308 Winchester.
Everything else is a bet on the strength of the gun and your hands. A 9 × 18 in a 9 × 19 gun can fire badly; a 7.62 × 39 won't fit a 7.62 × 51 and the other way round.
Tips from people who've handled it
- The base doesn't lie. A primer struck but not fired (a hang fire): keep the gun pointed in a safe direction for at least 30 seconds before opening. The round can still go off.
- A green primer or a case pitted with verdigris: don't fire it, it has taken on moisture.
- Eastern-bloc military ammunition often has corrosive primers (potassium chlorate): after shooting, clean the barrel with hot water, or it rusts within days.
- Storage: cool, dry, away from temperature swings. A military metal ammo can with a seal, and a desiccant sachet. Well stored, modern ammunition lasts decades. See Munitions — état, stockage, valeur.
- Weight: a thousand rounds of 9 mm weigh about 12 kg (26 lb); of .22 LR, about 3.5 kg (8 lb). That's why the .22 LR remains the most practical trade good of its kind.
- A cartridge thrown in a fire isn't a fired bullet: without a barrel, the case bursts and throws fragments, but the bullet leaves at low speed. Dangerous for the eyes, rarely more.
The law
In France, ammunition follows the category of the gun: buying it generally requires the same permit as the gun (shooting licence, hunting licence, authorisation). Rules vary widely from country to country. A gun or ammunition you find is reported to the police: see Une arme à feu trouvée.