What Caliber Is An AR-15? (Different AR-15 Caliber Options)

The AR-15 isn’t just a rifle; it’s a canvas of customization. Apart from the multitude of modifications you can make, you can also select from a wide selection of calibers it can be chambered in, from the versatile .223 to the specialized 9mm. It’s important to know the caliber of the AR-15 to ensure optimal functionality in terms of accuracy and user experience.

Once you understand the basics, you can delve deeper into the intricacies of different calibers for the AR-15, such as whether you can put any AR-15 upper on any lower, whether AR-15 barrels are interchangeable between different calibers, and whether you can change the caliber of an AR-15. Join us as we delve deep into the world of different AR-15 calibers!

What Is The Caliber Of An AR-15?

Below, we discuss the various cartridges fit for the AR-15.

Caliber Description
5.56 NATO / .223 Rem Lightweight with a flat trajectory, popular for rapid fire, excellent penetration, ideal for varmint hunting and self-defense.
.22 LR Minimal noise and recoil, perfect for beginners, affordable, widely available, great for target practice and vermin hunting.
6.5 Grendel Bridges gap between 5.56 NATO and 7.62 NATO, larger bullets for enhanced range, suitable for hunting big game.
300 Blackout Versatile, designed for better performance at shorter ranges, effective with suppressor, diverse load and bullet options.
6.8 SPC Improves 5.56 NATO’s terminal ballistics, better mid-range performance, ideal for medium-sized game hunting.
.224 Valkyrie Designed for extreme long-range shooting, impressive ballistics, supersonic past 1,300 yards, perfect for precision shooting.
350 Legend World’s fastest straight wall cartridge, less recoil, excellent for deer hunting, complies with restrictions in some areas.
9mm Transition from pistol to AR platform, mild recoil, suitable for self-defense and sports shooting in urban settings.

AR15 Caliber

1) 5.56 NATO / .223 Rem

Derived from the .222 Remington, the 5.56 NATO/.223 Rem is lightweight, producing a flat trajectory. It is one of my favorite varmint hunting cartridges because the ammo is relatively cheap yet powerful enough to take down coyotes and hogs.

Overall, the .223 Rem is the most popular AR-15 cartridge thanks to its excellent rapid fire and good penetration. This should be your first option if you’re thinking of buying an AR-15.

2) .22 LR

One of the oldest calibers and often hailed as America’s rifle, the .22 LR provides minimal noise and recoil, making it ideal for new shooters. Its affordability and widespread availability make it a top choice for target practice, home defense, and vermin hunting.

3) 6.5 Grendel

The 6.5 Grendel bridges the gap between the 5.56 NATO and 7.62 NATO. Its larger, heavier bullets offer enhanced range and kinetic energy, making it my #1 choice for hunting big game with the AR platform.

4) 300 Blackout

Developed from the .223 Remington case, this versatile cartridge was designed for better ballistic performance at shorter ranges. It’s especially effective with a suppressor and offers diverse load and bullet weight choices for various scenarios.

5) 6.8 SPC

Similar to the 300 Blackout, the 6.8 SPC (Special Purpose Cartridge) was created to improve the shortcomings of the 5.56 NATO in terms of terminal ballistics. It offers better performance at a mid-range distance, making it a favorite for medium-sized game.

6) 224 Valkyrie

Designed for extreme long shooting, the .224 Valkyrie is the pinnacle of AR-15 accuracy. This advanced rifle cartridge boasts impressive ballistics that stays supersonic past 1,300 yards. It’s truly a dream for precision shooters, allowing engagements at distanced once thought unreachable for the AR-15.

7) 350 Legend

Touted as the world’s fastest straight wall cartridge, the 350 Legend provides hunters an edge with less recoil than similar rounds. I must commend its deer-hunting capabilities – offering ample stopping power with minimal meat damage.

Additionally, it is compliant in areas where bottleneck cartridges are restricted and only hunting with straight wall cartridges is allowed, adding to its already great versatility.

8) 9mm

Synonymous with pistol ammo, the 9mm Luger’s transition to the AR platform reflects its global popularity. With lighter bullets and shorter barrel length, it has very mild recoil. This makes it ideal for self-defense and sports shootings, especially in urban settings where a short-barreled rifle is preferred, and over-penetration is a concern. Many of the AR-15 style pistols are chambered in 9mm as well.

The 9 mm’s balance of power and manageability demonstrates how critical the right caliber choice can be in meeting specific firearm needs.

Why Is The Caliber Of A Firearm Important?

The caliber of the firearm is important because it determines its recoil, range, effectiveness, use case, and, for hunters, the type of game it can hunt. The caliber impacts the rifle’s versatility, cost of shooting, and the shooter’s overall experience.

For instance, let’s say we need to decide between the .22 LR and .223 Rem. We first need to factor in our experience level with rifles – if we are novices, the .22 LR is better, but the .223 Rem is still a pretty solid novice AR cartridge.

AR-15 Caliber

Next, our use case: is it just target shooting, or are we going to hunt with it? While the .22LR’s ammo cost makes it better for target shooting, it is incapable of taking down deer. In comparison, the .223, being a more powerful cartridge, can comfortably take down deer at close to medium ranges.

Do you see where I’m going with this? All these factors that define a caliber are important before you buy it, and very important, always consider how the caliber will affect certain characteristics of the AR-15, such as barrel life and accuracy.

How Does The Caliber Of AR15 Affect Accuracy?

The caliber of AR15 affects accuracy due to variable ballistic characteristics. Factors like bullet drop, wind drift, and velocity all vary between different calibers and can affect accuracy, especially at longer distances.

These differences in caliber characteristics naturally lead to modifications in the rifle’s design, especially in the upper receiver, which is why you should also ensure both the upper and lower are compatible with each other.

Can You Put Any Caliber AR-15 Upper On Any AR-15 Lower?

No, you can’t put any caliber AR-15 upper on any AR-15 lower. While the AR-15 design favors modularity, not all AR-15 upper receivers are compatible with lowers due to differences in caliber size, bolt carrier groups, and magazines. But you can always interchange individual parts, such as AR barrels, when modifying your AR-15 upper and lower.

Do AR-15s Have Interchangeable Barrels For Different Calibers?

Yes, AR-15s do have interchangeable barrels for different calibers. However, when you interchange AR-15 barrels between different calibers, it is important to note that you might also need to swap out bolts and magazines because by changing the barrel, you are essentially changing the caliber of your AR-15. You need all AR-15 parts to match the new caliber.

Can You Change The Caliber Of An AR-15?

Yes, you can change the caliber of an AR-15. You can switch between calibers if you swap out the upper receiver group and sometimes the buffer system.

However, do your due diligence before changing the caliber, as it can have consequences, such as affecting the mountings and performance of the cartridge case.

Does AR15 Caliber Affect Optic Mounting?

Yes, the AR15 caliber affects the optic mounting. While it does not directly influence the optic mounting, the recoil and intended use of the caliber will influence your choice of optics and mounts.

For instance, a .223 AR-15 is best paired with an AR-15 red dot sight. Meanwhile, a magnified optic is ideal for long-range shooting .224 Valkyrie.

Can Hunters Use Optics On 300 Blackout AR15?

Using a 300 Blackout optic is sure to elevate your hunting experience. Whether hog hunting in the woods with a red dot sight or varminting coyotes with an LPVO, a 300 Blackout is ideal for various hunting optics.

Frequently Asked Questions

Can you use different caliber ammunition in an AR-15 rifle?

You can use different caliber ammo in an AR-15 rifle. But you should make sure you have the appropriate barrel, bolt, and magazine for the chosen caliber.

What is the most common caliber for AR-15 rifles?

The most common caliber for AR-15 rifles is the 5.56 NATO/.223 Rem.

The Bottom Line

The AR-15 is not just a rifle; it’s a platform offering immense versatility. With the ability to chamber various calibers, it caters to a wide range of shooting needs, from hunting to sport. Remember to always ensure each AR-15 component is compatible with one another and that you follow the appropriate safety guidelines when customizing your AR-15 rig. Happy modifying!

About the author

Charles Neser

I'm a life long hunter & gun lover. Currently pursuing my Master's Degree (M.Sc.) in Animal Nutrition at University of the Free State.

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