The firing of a bullet from a gun is the result of a series of mechanical and chemical processes. The bullet itself is composed of many parts: the casing, the primer, the gunpowder and the projectile. The only visible parts after the bullet is assembled are the casing and the projectile. Each part of the firing process must function without error for the bullet to fire properly.
At the base of the bullet is a small explosive; this small amount of explosive is what ignites the much larger amount of gunpowder. There are two common types of primers, rimfire and centerfire, and these names explain where the primer is located. On a centerfire bullet, the primer is located in the middle of the bullets casing, and the hammer strikes the center of the bullet. On a rimfire design, the primer is located all along the circumference of the bullet and the hammer strikes there to ignite the primer. Most modern guns are centerfire.
The firing pin is a long straight pin that strikes the primer cap, igniting it, and causing the bullet to begin its firing process. The squeezing of the trigger activates mechanical linkage attached to both the trigger and the firing pin. On revolvers, the hammer has a built in firing pin. The hammer, which is held back by spring pressure, swings forward to connect to the primer cap on the bullet. Without this action, the bullet would not function. Each manufacturer uses a uniquely shaped firing pin for forensic identification purposes. It is possible to tell what type of firearm fired a bullet by studying the indentation left on the primer.
The gunpowder, or propellant, is what provides the bullet with the energy to leave the barrel at a high speed. It is a common misconception that gunpowder explodes, but it does not. Rather, it burns extremely quickly. The chemical reaction of the powder burning creates expanding gases, which then create a huge amount of pressure. This pressure, trapped at the end of the bullet, forces the bullet out of its casing and accelerates it down the barrel. The amount of gunpowder affects the speed of the bullet. There are also ways for the bullet manufacturers to control the speed at which the powder burns, thereby affecting the power behind the bullet.
After the firing pin strikes the primer, the gunpowder is ignited, and the bullet leaves its casing -- accelerating extremely quickly down the barrel. The inside of the barrel has spiraling grooves on the walls. These grooves catch the expanding gasses and use them to spin the bullet at a tremendously fast rate.This rotation helps keep the bullet on a straight path to its target. The length of the barrel also seriously affects the bullets accuracy. Longer barrels keep the bullet on track for longer than shorter barrels, and are therefore much more accurate.
- Brand X Pictures/Brand X Pictures/Getty Images