Understanding Firearm Calibers and Gauges

We often receive questions about different firearms and calibers. Most guests want to know their best gun caliber for a particular purpose like self-defense or target practice. And of course it’s not always easy to answer, since there are many types of guns and ammunition available. Regardless of which type of firearm you use, understanding the basics about calibers, gauges and other terminology can help you improve your technique. We’ve compiled a few tips and definitions to help you make sense of common shooting terms. We’ll try to explain common shooting terms as simply as possible in future posts.

Understanding Parts of firearms

In order to understand the terminology of caliber and gauge, and so on, it’s important to know well about all parts of your firearm. For a new shooter, understanding parts of each ammunition can make it much easier to be adjusted. To make it easier, a better idea is to understand parts of each ammunition you want to use.


These are the parts that help a gun function. They are present in the guts of a gun. They allow the gun to load bullets, eject shells, and sometimes cock the hammer. These parts are activated when you pull the trigger. For example, a spring in a magazine, a hammer and cylinder in a pistol.


The stock is the part of the gun that connects it to your body and enables you to hold it. It also helps you to aim your gun and relax your hands while firing. ‘Stock’ is also a common nickname for the place on a weapon where you hold it when firing.

It has two parts: The Fore-end Part (a part of the rifle that attaches to the butt), also called the stock The Butt Part (the part of the rifle that contains the shoulder stock) It is a butt or buttstock that provides support to the weapon on your shoulder or hip. The fore-end is close to the buttstock and helps to align it for shooting.


The barrel is a cylindrical tube through which the bullet travels. It’s made of hard metal and can be found in nearly all firearms. When the trigger is pulled, gas is created through a gun pin that pushes the bullet down the barrel.


The word “bore” can have many meanings. In the shooting world, it refers to the inside of a firearm’s barrel. Most traditional shotgun barrels utilize a smooth bore. The inside of a smooth-bore barrel has a smooth surface. Rifling is a process of creating a grooved pattern on the inside surface of a rifle barrel. This process improves the stability of the bullet which helps it to travel in a straight line. In addition, rifling creates a torque on the barrel, so that the rotation of the bullet is guided by its spin. Rifling causes bullets to travel straighter than they would if they were not rifled and also increases their accuracy.


The word ‘caliber’ refers to a firearm’s bore diameter. The size of a handgun or rifle’s barrel is measured in millimeters or hundredths and thousandths of an inch. A 9 mm pistol has a bore that measures approximately 9 millimeters in diameter, and a .223 caliber rifle has a bore that measures approximately 223/1000 of an inch in diameter.

Since there are so many different types of bullets and barrel sizes available, it’s important to say approximately.

It’s difficult to give a definitive answer when it comes to gun caliber. There isn’t an industry-wide standard for denoting bore/bullet size. The so-called .30-06, the -06 has nothing to do with diameter of the barrel but instead was introduced to the US Army in 1906. The .30-06, .30-30, .308, and .300 Winchester are all 30 caliber rounds. But each one is a different size. When it comes to sizing calibers, there seem to be some exceptions to the rules.


When you hear the term “gauge” in shooting sports, it’s typically referring to a gun cartridge. Similar to caliber, gauge refers to the inside diameter of a shotgun barrel. In this case, the measurement is based on the weight of lead that can fit inside the barrel. While it may sound complicated, keep in mind that the smaller the gauge, the larger the size of the firearm’s bore. For example, a 12-gauge shotgun has a larger bore than a 20-gauge shotgun.

There are some exceptions to the gauge rule. For example, the .410 is measured by caliber rather than gauge.

Cartridge vs Bullet

“Bullet” and “cartridge” are often used interchangeably by many shooters and gun enthusiasts. Hang around a gun store or shooting range for a few hours, and you will hear this from visitors. However, the terms have different meanings. A cartridge is an entire unit that contains the primer, propellant, case and bullet. A bullet is a projectile that is propelled through the air by way of gunpowder.

Matching Ammunition

Despite what caliber or gauge you intend to use, always double check your firearm and ammunition to ensure that they match. All modern firearms should be stamped with the correct caliber or gauge on the barrel. Always double check to ensure that the firearm you are using is the correct caliber or gauge for the ammunition.