What Is a Cartridge and How Does It Work?

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If you’ve seen an action movie, you’ve experienced an actor shouting something like, “I need more bullets!” So, it’s no wonder that many people are confused about the right terms to describe ammunition. In short, a bullet is only one part of a whole piece. What you’re likely meaning to say is “cartridge.”

Before we dive in, let’s establish some common vocabulary and draw out the differences between each one so you don’t get confused.

  • Cartridge: A cartridge, also known as a round or a shell, is a complete unit of ammunition that contains all the necessary components for a firearm to function. It is a self-contained package that consists of four main parts — we’ll discuss these in detail below.
  • Ammunition: Ammunition is a broad term encompassing all types of projectiles and their accompanying components used with firearms. It includes individual cartridges and the associated supplies required for their use, such as magazines, clips, or belts. It also applies to shotshells (used in shotguns) or even specialty rounds like explosive or armor-piercing ammunition.
  • Bullet: Sitting at the top of the cartridge, the bullet is the component of ammunition that exits the firearm and hits the target. Bullets are usually made of a dense metal, such as lead, and are designed to be fired from a firearm.

The Four Parts of a Cartridge

A cartridge, often referred to in slang terms as a bullet, is the complete unit that gets loaded into the firearm. There are four distinct parts that make up the cartridge.

  1. Cartridge Case: The outer container which holds the gunpowder/propellent, primer, and bullet/projectile together. Centerfire rifle and handgun cases are usually brass, which is easily reloadable. Steel cases are sometimes used, usually in some military ammunition; these can also be reloaded but require special tools and techniques.
  2. Primer: This is the piece that ignites the powder charge. Sitting at the base of the cartridge, when the trigger is pulled, the primer creates a spark that ignites the gunpowder/propellent.
  3. Powder/Propellent: The powder or propellent is the fuel for the cartridge. As the propellant burns, it creates gases that rapidly expand and propel the bullet/projectile forward and out of the gun barrel.
  4. Bullet/Projectile: This is the top part of the cartridge that exits the muzzle and travels through the air toward the target. Projectiles come in many different shapes and sizes depending on the intended use.

How does the cartridge work?

Simply put, when you pull the trigger, the cartridge is loaded with everything needed to send a bullet down range in a single, self-contained package—this is a pretty big deal.

Back in the day, before cartridges were created, a person would have had to purchase the components separately and physically load the powder charge and projectile from the muzzle. The concept of self-contained cartridges emerged in the early 1800s, but it wasn’t until the 1840s and 1850s that practical and reliable designs were developed. 

Now that we understand what a cartridge is, let’s cover how the gun firearm activates the cartridge.

  1. A hammer or firing pin strikes the primer, which acts as the ignition source for the powder charge.
  2. The powder charge ignites and as it burns creates rapidly expanding gas, pushing the bullet away from the casing and down the chamber barrel.

We’ve got the basics down, but there are still some important things you need to know about each component. Let’s dive deeper into each part.

The Casing

As noted above, the “casing” refers to the shell that holds together all the other components. It’s often referred to simply as the “cartridge” or sometimes as the “brass.”

Some casings can be collected, reloaded, and reused after they’ve been fired. Reloading can save you money, but more importantly, for many people, the process allows them to tailor their ammunition to suit their individual needs and preferences.

Whether you want to reuse or recycle used casings, just make sure you have the right reloading supplies.

How to Clean a Case for Reuse

To clean a case, most people use a tumbler. Using a medium such as ground corncobs or walnut shells, the tumbling process removes grit and grime that would otherwise damage reloading dies and other crucial supplies. Done properly, the result is a shiny, polished case ready for reloading.

The Primer

At the base of a loaded cartridge is a primer which contains a very small amount of pressure-sensitive explosive, such as mercury fulminate, which acts as a primer. When you pull the trigger, the hammer strikes the primer, and it starts a chemical reaction that creates a spark, heat, and pressure in sufficient amounts to ignite the powder/propellant which will provide the primary force for the bullet/projectile.

Types of primers

In centerfire ammunition, primers are located in the center of the base of the cartridge; in rimfire ammunition, the priming compound is located in a specially formed rim around the base of the cartridge — we’ll discuss the differences between the two further down the page. There are two main types of primers, Berdan and Boxer.


Berdan is the older, traditional primer type commonly used in military cartridges. Berdan cartridge cases have multiple flash holes that allow for consistent and even ignition of the propellant. However, Berdan-primed cases are difficult to reload, so they are better for one-time uses.


Boxer primers are easily the most popular primer style manufactured in the United States. Boxer primers are used in centerfire cartridges and are easily reloadable. They have a centrally located anvil (The anvil provides the hard point against which the priming compound is crushed to detonate the primer) and boxer cases have a single flash hole in the center of the primer.

The Propellant

Once ignited by the primer, the propellant burns quickly, generating a large volume of gas. The gas rapidly expands, exerting pressure on the walls of the cartridge casing and the base of the bullet. This pressure forces the bullet out of the casing and into the barrel of the firearm.

In the past, black powder was used as the primary propellant in cartridges. In the modern era, nitrocellulose-based products (like smokeless gunpowder) are generally used instead due to their greater consistency and reliability.

Every type of propellant is designed for a specific purpose, usually suited specifically to handgun, rifle, or shotgun, based on large part on the burn rate (how slowly or quickly the powder burns). Some powders are optimized for pistol calibers, other powders are optimized for rifle calibers, and still other powders are optimized for use in shotshell ammunition.

Powder manufacturers spend a great deal of time and effort developing load data for almost every cartridge imaginable, so make sure you consult the appropriate reloading manual to help you choose the right powder for your cartridge.

Always check your manual

Check your reloading manual before developing a load and ensure you follow all recommended safety precautions. Your manual will identify the best powder charge and pressure for safe reloading and shooting. Deviating from the established guidelines can backfire on you (literally) in a big way.

The Bullet

The bullet, driven by the pressure of the rapidly expanding gas, leaves the cartridge, entering the barrel. Most modern rifle and handgun barrels include “rifling” – a series of lands and grooves cut in the barrel which spin the bullet and stabilize it during flight to increase accuracy. 

Once the bullet leaves the barrel, the gasses behind it escape and dissipate in the air while the bullet travels downrange to impact the target.

Sizes, shapes, and types

Bullets come in several different shapes, or “profiles,” depending on their intended purpose. Some examples are: 

  • Boat Tail Hollow Point
  • Jacketed Hollow Point
  • Round Nose
  • Soft Point
  • Spitzer
  • Flat Nose
  • Semi-Wadcutter
  • Wadcutter

A bullet’s profile can influence its stability, ballistic coefficient (which describes the aerodynamic efficiency), and even how it performs at varying distances. That’s why it’s important to first determine what your intended purpose is, whether it be hunting or target practice, before selecting your bullet.

Centerfire cartridges vs Rimfire Cartridges

The terms centerfire and rimfire determine where the primer is located and how a cartridge does its work.


Rimfire cartridges contain the primer within the rim or flange at the base of the cartridge. Firearms designed for these types of cartridges have a firing pin that strikes the rim of the cartridge to ignite the primer when fired.

Because of their design, these cartridges are generally for one-time use; while they can be reloaded, the process requires a few extra steps, and most shooters prefer to simply use new production rimfire ammo. Rimfire cartridges like .22 Long Rifle and other rimfire ammo is still extremely popular.


Centerfire cartridges use a separate primer that’s installed in the center of the casing’s base. Centerfire firearms are engineered to strike the center of the cartridge to ignite the primer.

The spark from the primer travels through a small hole in the center of the casing where it ignites the middle of the powder charge.

Order Your Reloading Supplies Today from Powder Valley

So, what is a cartridge? To sum it up, the cartridge is the casing, the primer, the propellant, and the projectile.

At Powder Valley, we carry a comprehensive selection of reloading supplies, tools, and accessories from the brands you trust, all at the lowest prices and with fast shipping.

Browse our online inventory and don’t hesitate to reach out if you have any questions. Our knowledgeable experts are here to assist. We’re happy to do everything we can to help you shoot more and pay less.