All About Ammunition

All About Ammunition

Components of Ammunition

A single piece of ammunition, made up of the bullet, casing, powder, and primer.
The metal projectile (usually lead) that is expelled from the mouth of a firing cartridge.
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.
The gunpowder used in a cartridge that propels the bullet.
A small cap in the head of the cartridge that, when struck by the firing pin, ignites the powder.

How Does Firing Ammunition Work?

When you pull the trigger of a firearm, the firing pin hits the primer and ignites the powder. As the powder burns, it creates pressure that pushes the bullet down the barrel.

How is Ammunition Measured?

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.

Popular Semi-Automatic Pistol Ammunition Calibers

.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.
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.
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.

Find a Range

The best way to learn about pistols is to get on the range! Use our Locator to find a range near you.


Learn more tips about training with your GLOCK pistols.