Pistols come in a wide array of types for a variety of purposes and needs. Here you can learn about pistol sizes, calibers, actions, and styles. Learn the working parts of a pistol, what makes it fire, need-to-know terminology, and more.

There are eight actions that occur as a pistol fires a projectile:

1. Feeding – Moves a cartridge from the magazine toward the barrel.
2. Chambering – A cartridge moves fully into the barrel chamber area.
3. Locking – The barrel and slide 'lock' together mechanically.
4. Firing – The cartridge primer is hit by the firing pin, powder is lit, pressure builds, and the projectile (bullet) leaves the barrel.
5. Unlocking – The slide and barrel mechanically separate slightly.
6. Extracting – The slide moves rearwards and the extractor 'hook' pulls the empty cartridge casing out of the barrel by its rim.
7. Ejecting – The ejector hits the empty cartridge rim, turning it/pushing it out the slide ejection port.
8. Cocking (resetting the action) – The trigger and the firing pin are set together and ready to fire another round.

What is the Action of a Gun?

The action of the gun consists of all the moving parts that facilitate the loading, firing, discharging of the empty case, and unloading of the gun. There are two types of action:

Double-Action:

A long trigger pull both cocks and releases the hammer/firing pin to fire the gun.

Single-Action:

The trigger is used only to release the hammer/firing pin and does not cock the firing mechanism.

Other Parts of a Pistol

Trigger

The trigger guard is the material around the trigger that provides protection and safety.

Hammer

The hammer impacts the firing pin or cartridge directly, discharging the ammo.

Firing pin

The firing pin is the hardened pin centered behind the primer of a chambered cartridge. When struck by the hammer, it impacts the primer cap of the cartridge and discharges the ammunition.

Ammunition

Ammunition is also known as a ‘cartridge’ or ‘round’. It consists of casing, primer, powder, and projectile.

Cartridge:

A single piece of ammunition, made up of the bullet, casing, powder, and primer.

Bullet:

The metal projectile (usually lead) that is expelled from the mouth of a firing cartridge.

Casing:

A tube that holds all the other ammunition components together, typically made from brass. The bullet is usually held in the open end of the casing.

Powder:

The gunpowder used in a cartridge that propels the bullet.

Primer:

A small cap in the head of the cartridge that, when struck by the firing pin, ignites the powder.

Ammunition is measured by the bullet’s diameter, which is known as “caliber”. The caliber can be measured in both inches and millimeters (mm).

Depending on where it was invented, ammunition is measured in millimeters or inches. 9mm ammunition originates in Europe, whereas the .40 caliber was invented in the United States.

Ammunition for a pistol corresponds to the pistol caliber, so you will use 9mm ammunition for a 9mm pistol.

.22 Long Rifle (LR):

Rimfire cartridge often used in sport shooting and training. This caliber is ideal for first-time shooters.

.380 ACP:

This small round is known as the “three-eighty” and is a popular choice for small pistols.

9mm:

This caliber is the most popular and widely used worldwide.

.40 S&W:

Larger and slower than 9mm, with more recoil.

.45 Auto:

Slightly larger and slower than .40 caliber, with a bit more recoil.

.45 GAP:

GAP stands for “GLOCK Automatic Pistol”. This caliber rivals the firepower of the .45 Auto, but is shorter, allowing it to fit into a more compact semi-automatic pistol.

10mm:

Has greater range and is faster than the .45 Auto.

.357 Auto:

Slightly longer than the .40 caliber, and known for accuracy and stopping power.