How Are Brass Cartridges Produced?

Rifle Ammunition

A brass cartridge is the largest part of ammunition. It holds the powder and the bullet, along with a primer in its end that is called the "rim." The rim is part of the "head," which leads to the "body" and then to the "shoulder" and the "neck" into which the bullet fits. When the primer is struck by the weapon's firing pin, it ignites the powder which creates a large amount of pressure in the cartridge. The pressure pushes the bullet out of the weapon's barrel and towards the target. Manufacturers produce cartridges to prevent them from bursting and causing flash-back that would otherwise hit the shooter. In automatic weapons, they must also be constructed to automatically eject and make room for the next cartridge.

Why Brass?

Ammunition manufacturers produce cartridges in copper, steel, aluminum but mostly in brass. Brass is a non-metallic alloy composed of 70 percent copper and 30 percent zinc. Under the extreme pressure caused by the ignition of the powder, cartridge cases expand before releasing the bullet. Brass cartridges are more expensive than those made from other metals, but because of their strength and their ability to withstand repeated expansions, they are the desired cartridges for ammunition re-loaders.

Types of Brass Cartridge

Brass cartridges are either manufactured straight walled or tapered. Straight walled cartridges are generally made for handguns and tapered ones, also called bottleneck cartridges, are typically used in rifles. Military ammunition will be constructed with thicker-walled cartridges than civilian ammunition to withstand the higher pressures of military loads. Brass is also used in larger military ammunition for tanks, ship guns, howitzers and the like.

First Stage of Production

Brass cartridges begin as round brass disks, known as "blanks," that are stamped out of metal strips. Through a series of stages, the blank is extruded into its cylindrical shape by squeezing it through a die under high pressure. Typically this process is repeated two or three times to achieve the proper length of the cartridge. In an older, more traditional method, the cartridge is "drawn" into shape by stretching it three to five times through a series of high pressure rams into a form die. After each draw the brass is annealed and pickled to harden the case.

Second Stage of Production

Once the cartridges have been extruded or drawn to their maximum length, they are trimmed and their necks and shoulders are formed. The shoulder is the part of the cartridge that tapers down from its body diameter to that of the bullet in a bottleneck cartridge. In rimless cartridges, an extractor groove is then machined and the primer pocket is created in the base.

Production Variations

With the variety of weapons available, ammunition manufacturers must produce their various cartridges to fit them. Depending on the weapon's mechanism, cartridges can be rimmed, rimless, semi-rimmed or rebated rimmed. Most modern auto-loading or bolt action repeating firearms use rimless cartridges to prevent cartridge jamming. Revolver cartridges and rim-fire cartridges are manufactured with rims.

References

• Accurate Shooter Bulletin: How Cartridge Brass is Made
• The Cartridge Case by Chuck Hawks