How Ammunition Works
The four parts of a modern metallic cartridge and the function performed by each.
Know what drives me crazy? When certain gun people get all cranky and attitudinal about new(er) shooters using the wrong word to describe some piece, part, or technique. If you’ve visited enough gun stores, you might have been the victim of this type of snobbery:
Joe or Jane Customer: “Hi! I need to buy a clip for my Glock!”
Cranky and attitudinal gun store clerk: “Sorry, we don’t have any Glock clips.”
Of course, the cranky and attitudinal gun store clerk knows the gun part the customer wants—a device that holds ammo in a Glock pistol—but because it wasn’t properly referred to as a magazine, he’s too snobbish to overlook the incorrect use of gun terminology.
The same thing happens with ammunition. Some people talk about buying or shooting “bullets,” while others use bigger words like “cartridge.”
The short explanation is that a bullet is just one part of a cartridge, so they’re not technically the same.
Personally, I don’t care if you call the stuff you load into your gun bullets or cartridges—I’m just happy you’re out shooting!—but in the interest of education and accuracy, it seems like a good idea to explore the whole topic and get really clear on what’s what.
And while we’re clarifying these terms, we can go a bit deeper and discuss exactly how a cartridge works and its exact relationship to a bullet.
Anatomy of a Cartridge
A cartridge is the proper term for a single round of ammunition. A modern cartridge includes four components: primer, case, powder, and bullet.
The primer is where all the action starts. It’s the small round metal object located in the center of the base of the cartridge. Just like the caps for a toy cap gun, a primer is filled with a chemical compound that explodes when it’s smashed.
So, when the firing pin—a rod that’s driven forward when you pull the trigger—impacts and dents the base of the primer, the compound inside of the primer explodes.
This (relatively) small conflagration creates a flame that is directed through a small hole and into the main body of the cartridge case, igniting the powder. (More on that in a bit.)
The case is the container that holds the powder. Think of the case as a container of sorts for all the other things that make up a cartridge. The primer fits into a small pocket at the base of the case; the powder resides inside of it; and the bullet is seated at the opposite open end of the cartridge case.
The case is the part that is flung out of your semi-automatic gun (or dropped or extracted from your revolver or bolt-action rifle) after you fire.
Cases are made of brass, steel, or aluminum, though some companies are successfully making cases out of polymer, more commonly known as plastic.
If you shake a cartridge, you’ll feel and hear something akin to sand rustling around inside. That’s the powder. Called “propellant” by gun geeks, it’s a specially formulated compound that burns really, really fast—faster than rocket fuel, or even marshmallows over a hot fire. In fact, it burns so fast that many people assume it explodes. We don’t need to get into the technicalities here, just know that this rapidly burning powder doesn’t technically explode. Rather, the fast burn creates hot, expanding gas that develops a lot of pressure really quickly inside of the cartridge.
All that gas has to go somewhere, so it follows the path of least resistance and pushes the bullet out of the case and down the barrel. As the powder burns, and pressure builds, the bullet moves ever faster down the barrel until it escapes the confines of your gun. The pressurized gases that escape the barrel just behind the bullet are what make a gun go BANG!
While we’re on the topic of burning powder, I’d like to note that we’re talking about really high levels of pressure. To put things in perspective, if you ride a spiffy racing bike, you know the tires are really hard because they’re pumped chock-full of air—somewhere between 80 and 130 pounds per square inch of air pressure. While that seems like a lot, it’s nothing compared to even a low-powered ammunition cartridge.
The .45 ACP load operates at pretty low pressure compared to other handgun cartridges, and even those generate between 15,000 and 20,000 pounds of pressure per square inch! Rifle cartridges like the .223 Remington used in AR-type guns hover around 55,000 pounds per square inch. By my math, I figure that’s about 611 racing bike tires crammed into that tiny little rifle cartridge.
At this point, the bullet part is pretty self-explanatory. It’s the only part of the cartridge that travels forward when you fire the gun. Also called the projectile, the bullet is what does the work downrange.
Bullets are made from different materials and come in various shapes and sizes. Most handgun bullets have a copper exterior (called the jacket) that surrounds a lead core. However, some bullets are made entirely from lead, while others might be made entirely from copper. The reason for these differences might be cost, or the desire for a specific effect when the bullet hits something.
Different bullets in the same caliber family might also be shaped very differently, depending on how you want them to behave. Rifle bullets for long-range shooting will be long and skinny, making them more aerodynamic and less affected by the wind. Self-defense or hunting bullets might be constructed in such a way as to expand when they strike their target. Match or competition bullets might get extra special attention during manufacturing to ensure that they are perfectly shaped, and each one is identical to the others. That ensures that each shot will hit exactly where it’s supposed to, assuming the shooter executes the shot the same way each time.
In some ways, the difference between the cartridge and the bullet is like the difference between a Saturn V rocket and the command module. With the Saturn V, there’s a whole lot of stuff below the capsule that serves no other purpose other than to get those folks in the capsule to wherever they’re going. In that respect, cartridges are like rockets: they’re a collection of components that, together, achieve the goal of launching a bullet or projectile downrange.
So head to the range and enjoy an afternoon of shooting cartridges!