(There’s a joke in the title there; if you didn’t get it right away, keep reading and it will hit you on the way out.)

In this article, I will discuss the components of ammunition: what they are made of, how they are put together, and what makes them go bang.

Types of Ammunition

First, let’s go over three basic ammunition types. The first two are reserved for handguns and long guns; the third, for shotguns.

Centerfire and Rimfire Ammunition

a centerfire ammunition case

The primer (the silver circle) is located in the center of the case, hence “centerfire.”

When discussing handgun/long gun ammunition, you will often hear the phrases “centerfire” and “rimfire.” These two terms, simply stated, refer to where the primer is located on the case. (We’ll get into the specific parts in a minute, so bear with me.) If the primer is located in the center of the bottom of the case, it’s known as “centerfire” ammo. Easy enough, right? “Rimfire” ammunition, as I’m sure you’ll be able to figure out, has the primer located along the inside rim at the bottom of the case.

The primer is actually a compound (paste, substance… whatever you want to call it). With centerfire ammo, the priming compound is located on the primer case. Rimfire has the compound itself inside the rim; there is no primer case, per se.

Shotgun Shells

Shotgun shells can also be considered centerfire ammunition, though you normally don’t hear the distinction because they are much more rare. (They exist, but are generally old and valuable, and therefore not really used much anymore.)

Parts of a Cartridge

centerfire ammunition cross-section

cross-section of centerfire ammunition

When lay people say “bullets,” as in, “How many bullets did  you buy?” they are actually referring to cartridges; bullets are just one component.

We’ve already discussed the primer, which contains a compound. Then there is the case, which is the frame of a cartridge; essentially, where everything is put together. The powder goes inside the case, and the bullet seats on the top of the case. So, the bullet is actually just one of the four pieces — the part that gets shot out of the muzzle of the gun.

Does that matter in the grand scheme of things? Nah, not really. If you are reloading ammunition then yes, it matters. Aside from that, it’s just a good piece of information to tuck away so you sound just as cool as the rest of the folks on the range.

A shotgun shell has all of these same components, plus an extra one called the wad. The wad is positioned in between the powder and the shot/slug — shot being several small, round pellets in lieu of a bullet, and a slug looking pretty much just like a bullet, but larger.

Wikipedia has the most concise explanation of what the was does:

The primary purpose of a wad is to prevent the shot and power from mixing, and to provide a seal that prevents gas from blowing through the shot rather than propelling it. The wad design may also encompass a shock absorber and a cup that holds the shot together until it is out the barrel.

How it All Works

Now that you have a fundamental understanding of the components of a cartridge, let’s talk about how it all actually works. When you pull the trigger of your firearm, the hammer/striker pin hits the primer. That priming compound sparks (for lack of a better term) and ignites the powder.

Before we go further, let me be clear. When I say “powder” as it relates to today’s commonly used firearms, I’m talking about a high energy, fast-burning propellant. It burns very hot, very quickly, and then dies. It’s not the same as black powder, which is explosive. Some firearms do use black powder — muzzleloaders are the primary example — so be careful when handling the powder for those firearms. But, generally speaking the propellant used for the purposes of our discussion will not explode Wile E. Coyote style.

Okay, back to the discussion. When the powder is ignited, it builds up a tremendously high amount of gas pressure, which forces the bullet off of and away from the case, down the barrel of your gun. This gas pressure also throws the slide back automatically on semi-automatic handguns and carbines, which starts the process of ejecting the spent case and loading a new cartridge for your next shot.

This is simplified, of course. After all, this article is just a primer. (Did you get the really bad pun yet?)

For rimfire cartridges, because they are so small and don’t have a separate primer case, the hammer/striker hits the rim of the case, which ignites the powder. The priming compound is injected along the entire inside rim of the case, since we obviously never know which part of the case will be struck.

Impress Your Friends… Knowledge Time!

An interesting point: the bullet itself is actually slightly larger than the bore (the inside) of the barrel. This is done on purpose, so when the gas pressure from the fired cartridge forces the bullet into the barrel, the bullet grabs onto the rifling inside the barrel, forcing it to spin. Just like a good quarterback throwing a pass, you want the bullet to spiral in the air.

This is also how all of the scientists on your favorite acronym TV shows are able to determine which gun a bullet was fired from. The rifling leaves an impression on the bullet jacket (usually copper), and every barrel is unique… just like snowflakes and our fingerprints.

 What Are Grains?

Perhaps the most confusing aspect of ammunition components is the term grain. This terms actually has two completely different meanings:

  • Grain can refer to the number of powder/propellant pellets that are loaded into a case. The more grains of powder, the hotter the cartridge’s load.
  • Grain can also refer to the actual weight of the bullet itself; not the whole cartridge, just the bullet. This is important, as you will find in time that you firearm prefers certain manufacturer and bullet grains over others. You definitely want to find the right combination to get the best accuracy and control from your firearms.

A Quick Word on Reloading

Reloading is the process of assembling your own ammunition. Using all of the components mentioned above and some specialized tools, you can build your own cartridges and shotgun shells. Both shotgun shells and centerfire cases can be recycled and turned into “new” cartridges. Rimfire, by the nature of their size and how the primer is struck, cannot.