How Does a Gun Work?


A firearm discharges when a spark ignites the powder in a chamber, creating enough energy to force a projectile through the barrel. Modern guns are somewhat more complicated in their operation, but the essence of how they fire a bullet or shot is the same as it was in eras of the past.

The Firing Pin

  • When the trigger is pulled, the firing pin of a gun is forced forward so it can strike against the cartridge, which is the metal—usually brass—that holds the bullet. The firing pin is prepared when the gun is cocked by pulling back the hammer or slide, or when a bolt or pump is pulled back and thrust home.

The Shell

  • The back of the shell, or the end opposite the bullet, contains primer. The primer is ignited when the firing pin forcefully hits the shell. In centerfire ammunition, the primer is placed in the center of a case in the shell. In rimfire ammunition, the primer covers the inside rim of the shell. When struck, the primer sparks, which ignites the powder located between the primer and the bullet. That ignition causes gases to expand toward the front end of the barrel of the gun.

The Projectile

  • The projectile stands between the expanding gas and the front of the barrel. Projectiles are typically single bullets, but in shotguns they may be groups of small lead balls known as shot. Bullets for rifled guns are slightly larger around than the diameter of the barrel to ensure that they rub on the barrel’s interior.

The Barrel

  • Modern rifles and handguns have rifled, or grooved, barrels. These grooves cause the bullet to spin as it leaves the gun. This spinning helps ensure that the bullets do not curve in flight. The principle is the same as a quarterback putting spin on a football as it is thrown. Shotguns have smooth barrels since they are designed to fire shot. The smooth barrel allows the shot to spread out after leaving the gun, making it easier to hit a fast moving target, such as a duck or rabbit, or to cause more trauma to a slower target.

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