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Cartridge Cases

Home > Propellants, Firearms, and Ammunition Development > Ammunition > Cartridge Cases

The modern cartridge case serves several important functions:

  • Contains the other components (projectile, primer, propellant) in a single unit for convenience of handling and loading
  • Resists the firing-pin blow during ignition
  • Forms a gas seal (obturation)

Paper powder charge

In the earliest days of small arms, cartridges began to evolve as an alternative to the slower process of handling a powder flask for charging each shot. In a rudimentary cartridge, a charge of black powder was measured into a thin paper or linen tube that was slightly smaller than the bore.  A ball was then placed on top of the powder in the tube and secured with glue or a string.

Early breechloaders incorporated a sharpened cutter blade atop the breechblock. A paper cartridge was loaded, but when properly seated, stood slightly out of the barrel. When the shooter closed the action, the cutter sheared off the rear of the cartridge, exposing propellant to the flash hole. This eliminated misfires caused by excess paper blocking the flame from the percussion cap.

digram of ammunition

Burnside cartridge

Image Courtesty of International Ammunition Association

The Burnside rifle used an unusual brass cartridge that was largely supported by the breech rather than the barrel. A small covered hole in the base of the cartridge received the blast from the percussion cap; the seal burned through, igniting the powder charge. The Burnside cartridge walls were stiff and did not expand sufficiently to seal the bore.

The true modern cartridge is flexible enough to expand under pressure and completely seal the rear of the barrel, yet strong enough to remain intact at peak operating pressure. Its diameter must be slightly smaller than that of the chamber to keep the cartridge case wall expansion to a minimum. The length dimensions have to match the chamber’s corresponding support surfaces so that the case can withstand the blow of the gun’s firing pin.

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