If you have ever been to a gun store, you will notice that there are numerous types of ammunition. Boxes on top boxes of different branded ammunition with different gun caliber designations. You might wonder where one might start.

I would start with the firearm you are looking to purchase and do some research on the type of ammo it uses. You might also want to do research on other guns to get a feel for what is pretty common in the gun community. Many firearms use commonly used ammo which is usually pretty inexpensive. Usually the fire arms that are most common are Semi-Auto handguns. Some firearms have special gun calibers which can be expensive and/or hard to find.

Let’s dive into some ammo history to see what gun calibers are the most popular.

Most popular semi-auto handgun calibers


Also known as 9mm Parabellum or 9mm Luger. This caliber has been toted as the “the world’s most popular and widely used military handgun and sub-machine gun cartridge” by the 2014 edition of Cartridges of the World. You will see many firearms fitted to this caliber due to it’s smaller size and decent stopping power. Due to it’s popularity, 9mm is also inexpensive. It’s been used since the early 1900s and easily the most used today.

.45 ACP

This is a quite bigger round compared to the 9mm. This ammo type got famous right before The Great War and has been used since. “ACP” stands for Automatic Colt Pistol and was design as a replacement to put in .45 Colt Revolvers and used with famous guns like the Colt 1911 and the Thompson sub-machine gun. It might fire slow compared to other rounds but stopping power is sufficient due to it’s size.

.22 LR

For those looking for a true beginner round, look no further. The .22 LR round is small and light round generally used for hunting small game in the hunting world. It has been fitted to be used in a wide variety of different guns including semi-auto pistols, revolvers, and rifles. Since the size of this round is small, recoil is kept to a minimum which makes it great as training ammunition.

Practicing with caliber

Choosing a gun based off caliber mainly comes down to what you are going to do with it. Your general purpose of your firearm will determine what caliber to get in a firearm. This will also mean that you need to be comfortable with the caliber the firearm is chambered in.

Practice shooting can go a long way in getting to know what round feels comfortable. Practice shooting with multiple calibers with different guns if you can. Try going to the range and renting some different guns so you can get a feel for what you might like.

Gun shop employees also have good knowledge of where to start and recommendations of what guns and ammo types to try. Ask around to get some recommendations and further understanding of what guns and calibers will work best for you and your purpose of your intended firearm purchase.

Different sizes equals different purpose

The purpose of different sized ammo is pretty simple – the bigger the bullet, the bigger the target. Generally, if you choose a caliber that is larger, expect to be using this on a larger target. A larger round usually means more noise and gun recoil. It could also mean using a larger gun to support this specific caliber. For example: The .44 Magnum cartridge has been known to kill elephants while the .22 LR (half the size) is know to kill much smaller game like rats and other pests. Firearms designed to used a .44 Magnum are usually very large handguns. Firearms chambered in .22 LR are usually smaller with much less kick.

The purpose of different sized ammo is pretty simple – the bigger the bullet, the bigger the target

What caliber is middle-of-the-road

You might get a different answer depending on who you ask when it comes to a caliber that is considered “not too big and not too small”. I would guess most gun enthusiasts would say that 9mm is the most middle-of-the-road due to it’s small size, adequate stopping power, and affordability. 9mm is very common choice for beginners, veterans, those on duty, and self-defense. Starting here at 9mm and moving to other calibers would be a great way to start your gun journey.

How ammunition caliber is designated and measured

You may wonder why ammo is either designated by measurement in metric (usually in millimeters) or by caliber (the diameter of the barrel of the gun). It has usually depended on the time period on which the ammunition was adopted.

New ammo types usually use metric measurements due to the fact that manufacturers conform to NATO (North Atlantic Treaty Organization) specifications. NATO is comprised of many nations that use the metric system so designating ammo in millimeters is ideal.

Ammo that is designated in numeric decimal caliber means that the round is measured by the bore of the barrel in a decimal of the inch. For example: .45 caliber bullets shoot out of gun barrels that are .45 of an inch in diameter.


It’s up to you to choose what you want. You have to address a couple of things when you make your decision. These factors might include purpose, cost of weapon, cost of ammo, and upkeep. Feel free to ask anyone knowledgeable about the subject. Make sure you practice a lot to understand more about what you are getting into. Remember, Practice Makes Proficient.