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AR-15 Caliber Guide

AR-15 Calibers Demystified: What Caliber is an AR 15 and Which One is Ideal for Your Needs?

As one of the most versatile and capable rifle calibers, the AR-15 is a semi-automatic rifle designed with an unwavering focus on flexibility, speed, and power.

Built to be as lightweight and powerful as possible, the AR-15 platform enjoys a massive range of calibers.

From small .22LR plinking bullets to the almighty .458 SOCOM rounds, the AR-15 eats many types of different cartridges with various characteristics. Hence, most people have problems deciding which AR-15 rifle caliber is the best one of them.

In this guide, we will answer all your questions regarding AR-15 calibers, and find the most suitable one for you.

What is Caliber?

Terminologically speaking, ‘caliber’ refers to the diameter of a gun’s barrel bore that can be measured either in inches or millimeters. That’s why it’s usually considered the terminology for bullet size.

However, the AR 15 caliber size and bullet size conundrum are misleading because different cartridges oftentimes use the same caliber, but they are not interchangeable. The most famous example of this is the .223 Remington and the 5.56×45 NATO, as well as the .22-250 caliber.

The Difference Between ‘Cartridge’ and ‘Caliber’

The difference between ‘cartridge’ and ‘caliber’ is that ‘cartridge’ is the full overview of the ammo’s characteristics, not just the diameter of the bullet, while ‘caliber’ only refers to the diameter of the barrel bore.

That’s why it’s important to know the specifics when you’re shopping for ammunition for your AR-15 rifle

What Caliber Is an AR 15?

What caliber does an AR 15 take is purely a question of purpose, not just dimensions and characteristics.

Generally, the AR-15 rifle is chambered in the .223 Remington or the 5.56×45 NATO caliber, usually nominated as the ‘.223/5.56’. It’s, without a doubt, the most popular AR-15 caliber on the market.

Aside from that, there are many other compatible variants, like the .223 Wylde, .22LR, 7.62x39mm, .308 Winchester, and the .50 Beowulf, as one of the most powerful AR 15 caliber bullets.

You can even find an AR-15 rifle that can run a 9×19 Parabellum cartridge, oftentimes modified with a pistol kit that can be easily customized to your whim.

Here’s an incomplete but common list of cartridges that the AR-15 rifle can run:

This is what makes the AR-15 a versatile platform for many applications.

Best AR 15 Long-Range Calibers

When long-range applications are in question, the AR-15 rifle generally shoots well around the 100- to 300-yard range.

Truth be told, there is no absolute best long-range AR 15 caliber. However, here are some of the best long-range calibers that make it feel like the AR-15 rifle is practically designed for long-range applications.


While there are differences between these cartridges, they’re commonly regarded as the same, only the 5.56 NATO being more powerful. The .223/5.56 is lightweight, has low penetration, and is a solid choice for home defense.

When it comes to practical long-range use, you’re able to shoot up to 200 yards with your AR-15 rifle, but it’s recommended that you go for the 50- to 150-yard distance as a common rule of thumb.

6.5 Grendel

The 6.5 Grendel cartridge is overall regarded as the best AR 15 caliber for hunting, and for a good reason, too. It has much more energy than the .223/5.56 caliber and has far less recoil than the .308 Winchester caliber.

Some folks like to think that this bullet can be effective up to a thousand yards but with solid terminal statistics. But don’t expect to reach as far, as this depends on the rifle customization, barrel threading, bullet manufacturer, and other factors.

.308 Winchester

Most hunters consider the .308 as one of the best hunting calibers because it offers decent power, and long-range applications at the 800-yard mark. However, it’s very expensive and only reserved for the most seasoned hunters. Good luck finding it in the ammo stores!

AR 15 Calibers for Protection & Defensive Purposes

For self-defense and home defense, you really need to pick an AR-15 platform that runs cartridges with significantly minimal penetration power. This is a very important point to consider, especially when it comes to self-defense and maneuvering tight corners.

There’s only one way to determine a good caliber for self-defense, and it’s pistol caliber kits.

AR-15 Pistol Calibers

What makes the AR-15 rifle so popular as a platform is its decent ability for 9mm and .45 ACP chambering. The purpose is obviously home defense application, not just bullet availability.

To turn your AR-15 platform into a pistol caliber, you’ll need a decent pistol caliber kit that will allow you cross-platform compatibility and the convenience of using an 8-inch or 10-inch barrel for home defense purposes.

Things to Consider When Choosing the Right AR-15 Caliber

Besides the purpose of the caliber of AR-15 rifle platforms you’ll be using, there are lots of factors to keep in mind when picking a suitable AR-15 bullet.

We’ll focus on the two main points any AR-15 enthusiast should consider.

Availability of AR-15 Kits and Conversion Parts

While it’s easy to find 5.56/.223 chambering parts and ammo for your AR-15 rifle, finding the proper conversion parts is going to be an issue, especially when you’re looking to try out different calibers.

You need to make sure that you stick with a certain kind of ammo for your chosen caliber because some can be more specialized for different purposes like hunting or sporting.

The Price Tag

The AR-15 rifle isn’t expensive when it comes to picking one on the online or local firearm shop.

Even though you won’t need to pick one that’s worth a thousand dollars, it’s recommended that you aim for a higher price tag. There’s a reason why some AR-15 rifles cost $300, and some cost $5,000.

Remember, what you pay for, is exactly what you get. We recommend you aim for the $500-$1000 price range if you want absolute reliability.

Conclusion: The AR-15 Is a Flexible Platform for Most Applications

We hope that this clears up any questions you had about AR-15 caliber purposes, whether it’s about short or long-range applications, self-defense, or sporting.

Granted, there is so much more to talk about the AR-15 rifle and its impeccable cartridge versatility. For now, we hope that the guide helped you narrow down your cartridge choices.

Feel free to contact us any time at Mid State Firearms, and we can help you pick a proper caliber. We recommend you browse our wide variety of AR-15 rifle kits, upper receivers, and bolt carrier groups as well, so you can see which one suits you best.

Stay safe, shoot straight.

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