Brass Sheet Metal
Shell casings for small arms ammunition begin as several hundred feet of brass sheet metal strips. Brought from foundries in massive coils, the brass strips are loaded by crane into an uncoiling machine. The metal first runs through a series of rollers to remove any curvature from the strip. Next, a hydraulic press cuts 2- to 3-inch-wide disks from the brass and stamps them into a vague "cup" shape.
Stamping and Annealing
While a strong metal, brass can also be considerably brittle. To prevent the cupped brass disks from cracking during the shell-casing manufacturing process, each piece is passed through a row of extremely hot flames between stampings. These flames heat the brass until it is literally glowing "red hot," at which point the pieces are removed and allowed to cool. Known as "annealing," this heating process allows the alloy's strained crystalline structure to rearrange itself. After cooling, the cups are placed into a specially shaped metal hole called a "die" and stamped again, bringing them closer to their final shape. Again, the cups are annealed to reduce internal strain. This stamping-annealing cycle repeats two or three more times before the brass reaches its final shape: a perfectly cylindrical cup with a flat bottom.
Washing and Polishing
Once the final annealing is complete, the shell casings are poured into large rolling vats where a constant stream of water and detergent wash any grit, grease or soot from the metal. Next, the shell casings are rinsed and loaded into a special rotary polisher.
The cylindrical cups then pass through a machine that imprints the bottom surface with caliber information and a small, perforated disk through which the spark from the hammer will be able to reach the powder inside the shell. Finally, a machine will cut a ridge around the shell near the base. This ridge, known as the "ejector groove," is what the gun latches onto in order to expel empty shell casings once its round has been fired.
Necking and Annealing (Rifle Bullets Only)
For rifle ammunition, the opening of the cup must be gradually narrowed. To achieve this, the shell is stamped through a series of dies that reshape the edge in small increments. Just as before, the shells are annealed between each stamping.
Washing and Lubricating
Finally, the shells (both handgun and rifle) are washed, rinsed and run through a lubricating machine. The shell casings are now ready for powder and lead rounds.