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Cartridge (firearms)

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A cartridge, often called a round, is a pre-assembled unit of ammunition. It is a vital invention for modern firearms. A cartridge combines several parts into one package. These parts include a projectile, a propellant, and an ignition device. The entire assembly is held inside a case made of metal, paper, or plastic.

Cartridge cross section
Cartridge cross section

While many people use the word "bullet" to mean the whole package, that is technically incorrect. In precise terms, a bullet is only the projectile itself. The cartridge is the complete system that allows the projectile to be fired safely and efficiently.

To understand how a cartridge works, we must look at the sequence of a single shot. First, the cartridge is inserted into the chamber of the gun. It must be aligned with the bore axis, which is the path the projectile travels. When the trigger is pulled, a mechanism releases a hammer or striker. This causes a firing pin to strike the primer at the base of the cartridge.

Centerfire & rimfire ignition
Centerfire & rimfire ignition

The primer contains a shock-sensitive chemical. This impact creates a jet of sparks that travels into the case. These sparks ignite the main propellant charge, such as smokeless powder. This rapid combustion, called deflagration, creates highly energetic, high-pressure gases. The pressure builds until it overcomes the friction holding the projectile in the case neck. The expanding gases then push the projectile down the bore and out of the muzzle at high speed.

Modern cartridges are categorized by how the primer is positioned. These different designs are known as primer types. In a centerfire cartridge, the primer is located at the center of the case head. In a rimfire cartridge, the primer is located inside the rim of the case.

Rim fire
Rim fire

Historically, there were many other types, such as pinfire, cupfire, and teatfire. However, only centerfire and rimfire designs have survived into the modern era. Each type requires a specific mechanism in the firearm to strike the primer correctly.

Before the cartridge was invented, loading a firearm was a slow and difficult process. Shooters had to load projectiles and propellant separately through the muzzle. They also needed a separate source of activation energy, like a slow match or a percussion cap. This method was clumsy and restricted the rate of fire. It also made logistics difficult because many parts had to be carried. The invention of the cartridge specifically for breechloading firearms changed everything. It provided an "all-in-one" package that is easy to transport and load quickly. This innovation helped protect the propellant from moisture and contamination.

Every cartridge has four main components: the case, the projectile, the propellant, and the primer. The case is the most defining part. It acts as a container and a protective shell.

Many bullets
Many bullets

Cases can be "bottleneck" shaped or "straight-walled." A bottleneck case has a wider body and a narrower neck, separated by a shoulder. Some designs include a "ghost shoulder" to help the cartridge line up more accurately. The case also helps the gun function. In self-loading firearms, the case allows the mechanism to use propellant energy to load new rounds automatically.

Cartridges are also grouped by their overall length, or COL. This measurement determines the size of the firearm's receiver. Mini-action cartridges, like the .223 Remington, have a COL of 2.25 inches or shorter. Short-action cartridges, such as the .308 Winchester, have a COL between 2.25 and 2.8 inches.

Cartridge Sample 2
Cartridge Sample 2

Long-action cartridges, like the .30-06 Springfield, have a COL between 2.8 and 3.34 inches. Finally, magnum-action cartridges, such as the .375 Holland & Holland Magnum, are longer and wider, with a COL between 3.34 and 3.5 inches.

Material choice is important for the durability of the case. Brass is the most popular material because it resists corrosion. It can also be work-hardened to handle high pressure or annealed to make it soft enough for reloading.

Handguncalibercomparison
Handguncalibercomparison

Some military forces use steel cases because steel is less expensive. Steel is lighter, which provides a logistic advantage for soldiers carrying large amounts of ammunition. However, steel is more prone to rust and can be harder to extract after firing. Aluminum and plastic are also used in specific types of ammunition, such as shotgun shells.

Not all cartridges function perfectly every time. If a cartridge fails to ignite, it is called a "dud." If it ignites but does not push the projectile out of the barrel, it is called a "squib." There are also "blanks," which are cartridges without a projectile, and "dummies," which are completely inert for training purposes. Understanding these distinctions helps explain the complex science of modern ammunition.

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🖼️ Images & Media (30)
File:Cartridge cross section.svg
Cartridge cross section.svg
File:Cartridge Sample 2.jpg
Cartridge Sample 2.jpg
File:Big caliber cartridge comparison withDATA.jpg
Big caliber cartridge comparison withDATA.jpg
File:Many bullets.jpg
Many bullets.jpg
File:Powder Samples.jpg
Powder Samples.jpg
File:Percussion caps.jpg
Percussion caps.jpg
File:Centerfire & rimfire ignition.gif
Centerfire & rimfire ignition.gif
File:Berdan vs boxer2.jpg
Berdan vs boxer2.jpg
File:0.30-30 Winchester case, stages in the drawing process, book; Cartridge Manufacture (1916), author; Douglas T. Hamilton.png
0.30-30 Winchester case, stages in the...
File:US paper to centerfire rounds.jpg
US paper to centerfire rounds.jpg
File:Festungsmuseum Reuenthal Sonderausstellung Zuleger britische Patronen.JPG
Festungsmuseum Reuenthal...
File:Chassepot paper cartridge.jpg
Chassepot paper cartridge.jpg

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