How Does a Cartridge Work? The Story Behind Ammo

How Does a Cartridge Work? The Story Behind Ammo

When non-shooters talk about firearms, most know but don’t fully understand that a gun is a system, consisting of the shooter, the gun itself, and the ammunition. Much focus is given on the first two parts of the system, and correctly so. However, without ammo, a gun and a shooter is just a person with a bunch of metal, wood, and polymer cobbled together in a complicated way.

Today, the vast majority of modern ammunition comes in the form of “cartridges”, also known as “self-contained ammunition.” Unless you shoot with muskets, (as might be the case for thousands of Revolutionary War enthusiasts and reenactors here in Philadelphia) and other unusual firearms, modern cartridges are likely to be the type of ammunition you’re most likely to come across for hunting, self-defense, and recreation.

While this won’t be a deep dive into ammo—that would take a whole library of books to cover, and then some—we’ll give you the basics behind modern ammo and why it can matter to you as a shooter. If you’re in the Philadelphia area like we are, be sure to buy ammunition in Philly from these trusted sources.

Why Cartridges? 

Early black powder firearms did not use self-contained ammo. That is, the projectile, powder, primer, and wadding (if needed) had to be loaded separately into the gun before it could be fired successfully with some kind of ignition device. While black powder firearms were more than sufficiently deadly and were capable of defeating plate armor and even stone fortifications, the process of loading them was slow and cumbersome.

To add to this, having all these components separated made them prone to contamination and led to reliability issues. When insufficient attention was given, the powder could become wet and lead balls could become deformed, which could lead to reliability issues when the time came to use them.

What’s more, loose gunpowder (especially black powder) is especially volatile. Unintended shocks or exposure to heat was often enough to set off the powder, which often led to disastrous results for the shooter and those around them.

Modern self-contained ammunition sought to solve all those problems. By having the bullet and propellant powder all in one self-contained metal “bottle,” loading a weapon could be made faster and more reliable. The development of modern propellant powder and separate explosive primers into cartridge design also made ammunition far safer to handle and ran far less of a risk of accidental discharge.

Having self-contained ammo in cartridge form also led to other developments. As the performance of cartridges can be made extremely repeatable, designers soon realized the recoil power of the ammo could be reliably harnessed to load a subsequent round into the chamber and eject the spent cartridge at the same time.

This led to the development of truly practical repeating arms that did not require an extraordinary amount of work to load. It could be said that modern automatic and semiautomatic man-portable firearms as we know them would not be possible without modern cartridges.

Key Features of Cartridges

Save for very few exceptions, modern cartridges are made of a bullet at the business end, an explosive primer at the rear, a relatively stable secondary propellant charge inside, and a metal case to hold the entire assembly together. Each of these components may have additional parts or variations, such as different cores, tips, divots, and jackets on the bullet. However, by and large, these basic components are what you can expect from modern ammunition.

Most cartridges are either rimfire or centerfire. Rimfire rounds are less common but are still around due to the popularity of .22 Long Rifle as an extremely affordable practice and varmint extermination round. These types of ammo have their primer located in their flattened rim, as a rimfire weapon’s firing pin strikes the cartridge towards the edge of the case bottom. Centerfire rounds are by far the most popular for all other purposes outside of those mentioned for rimfire. With these types of cartridges, the firing pin strikes the center of the case bottom, where a reloadable primer is seated.

Most commercially available cartridges use variations of centerfire ammunition technology. Most rounds that are considered practical for personal defense, hunting, and precision shooting tend to be centerfire ammo. Their design with a separate primer component makes them somewhat more reliable compared to rimfire ammo, where small manufacturing errors can easily cause duds or misfires. They also tend to be preferred by serious firearms enthusiasts because, for the most part, they are easier to reload and therefore customize.

Innovations in Cartridges

While the basic concept is solid which is why cartridges have been virtually unchanged for the past 150 years—revising and even omitting different aspects of each of their few parts can lead to cartridges with wildly different performance envelopes.
Changes in these component designs can also determine the form factor of the firearms that use them. For instance, modern rifles that use 5.56mm and 7.62 NATO are designed around the concept of an “intermediate cartridge” that’s heavier-hitting than a pistol round and had most of the power of a “full-powered” rifle round like .308 Winchester, without all the weight and excessive recoil of the latter


Today, cartridges continue to be reinvented in the context of their use. Environmentally friendly cartridges, for instance, may soon be making their way to your neighborhood shooting range, as well as other places where the high accumulation of lead may pose issues to the soil and groundwater. New propellants and materials for cases and bullets are also being experimented with to reduce weight and to improve muzzle velocity and performance without impacting the shooter. New bullet designs are also being investigated for defeating body armor, which is starting to become prevalent even in asymmetric warfare.

There are many things about firearms that are endlessly debated, and joining these “discussions” is part of the fun for some people in the firearms community. However, the basic concept and layout of modern cartridges is something that most people on any side of any firearms debate will agree is a good thing.

Whether you already do some shooting yourself or are simply interested in learning more about how guns work, it’s great to know a bit more about the modern self-contained ammunition. The context behind their development, and the near limitless innovations within the constraints of their relatively small and simple layout, and even the way they have changed modern life as we know it have all been the subject of countless hours of both serious scholarship and casual discussions. And it’s likely to continue this way for at least a few hundred more years.

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