AR-15 Calibers Overview [Which is Best For You?]

What a lot of people really don’t know is that the AR-15 is truly one of the most versatile platforms ever designed. Normally chambered in one of three or four cartridges, it can actually handle dozens more.

Here is a pretty long list of some awesome options that you may not know are even available.

Some of these are awesome, some of these are standard, all of them are interesting!

Most, But Not All

Before we get to the list I want to throw a little disclaimer in here. Yes, I know this is not every single cartridge that you can find for the AR-15.

Some of these are basically extinct, some of these are super common, and there are a dozen or more others that didn’t make it on our list.

Most of the ones we’ve left off are wildcats, some of them are just very minorly modified versions of something that is on the list, some of them are just so unobtanium and uninteresting that I didn’t feel like doing the jazz hands on my keyboard to talk about them.

If your favorite cartridge you’ve ever shot isn’t on the list, tell me about it in the comments! Just please don’t get mad that we didn’t include it.

Make a good enough case as to why it should be included and maybe we’ll add it in ;)

AR-15 Rifle Cartridges

General Purpose / Multi-Role

223 Remington / 5.56 NATO

If you don’t know much about the AR-15, you should at least know that .223 Remington/5.56 NATO is the OG standard for the platform.

It’s actually pretty rare to find an AR-15 actually chambered for just .223 Remington these days, most are chambered for 5.56 NATO or 223 Wylde and can fire .223 Rem and 5.56 NATO ammo just fine.

This is a great do-all option that does well in everything from home defense to hunting game.

While this would never be my first pick for something like deer, it can be used for deer -- if it’s legal in your state.

What 5.56 really shines in are roles that are more people-related. Be it competition, training, or personal defense.

[Shop 5.56 uppers and more from Bear Creek Arsenal!]

7.62x39

The classic AK-47 cartridge has been adopted to the AR-15 more because we can than anything else.

Historically, 7.62x39 really didn’t work that well in the AR-15. Bolts were a lot less durable, feeding and ejection issues were common, and the magazines were weird at best.

Because of those issues and the fact that 7.62x39 was so perfect in an AK, AR-47s as they were often called got a bad reputation.

That was the past though.

Bear Creek Arsenal has made a number of design changes and enhancements like an improved bolt, enhanced firing pin, and better magazines that have pushed the AR-47 forward in a huge way.

These days, with the right setup, 7.62x39 can run outstandingly well in an AR -- both brass- and steel-cased ammo!

[Shop 7.62x39 uppers and more from Bear Creek Arsenal]

.22 Long Rifle

A lot of people look down on the humble .22 LR but it has a deserving place in everyone’s armory.

For the AR-15 .22 LR is really handy and fun. From training new shooters to hunting small game, .22 LR has a long list of uses and it does all of them at a much cheaper price than any other AR-15 cartridge can.

Personally, I love to use .22 LR uppers for training. Firearm manipulation and close distances shooting are both great ways to use .22 LR to train while keeping your budget a lot smaller than if you used 5.56 NATO.

For a lot more info and some recommendations, take a look at our Complete Guide To The AR-22!

Hunting Large Game

.350 Legend

Most states don’t care what shape your rifle cartridge is in, but there are a few that do. Why? Probably the same reason California thinks a flash hider makes the rifle more spooky.

For those odd duck states that believe deer should only be harvested with straight wall cartridges, the .350 Legend was created.

Ballistics closely match 300 Blackout making this basically a sub-250 yards deer puncher.

It isn’t cheap, there isn’t a lot of ammo for it, and outside of those weird law states -- there isn’t a real need for this round to exist.

But for those that need it, nothing else will do.

[Check out our 350 Legend guide for more information about the caliber.]

.450 Bushmaster

Designed for big game, .450 Bushmaster puts 12ga slug power in an AR platform. Bourn out of Jeff Cooper’s mind, this big honker of a cartridge is great for putting down any sized animal in North America.

Just make sure to get fairly close because this has the ballistics of a lead rainbow.

You’ll get loads of power upfront, but it drops faster than an Astro’s OPS without the trashcans.

[Check out our guide to 450 Bushmaster ballistics here!]

.458 SOCOM

Maybe the coolest origin story of any AR-15 cartridge, the .458 SOCOM was designed because of veterans of Operation Gothic Serpent telling firearms developers that there needed to be an AR-15 cartridge with more power.

Something they don’t tell you in the movie Black Hawk Down is that many of the hostile forces that Delta Force and the Rangers faced in Somalia used a local drug called Khat, basically, a stimulant that helped them ignore pain and wounds.

Ballistics are almost the same between .458 SOCOM, 50 Beowulf, and .450 Bushmaster -- but .458 SOCOM has the benefit of being designed with the intent of as little changes to the standard M4 as possible.

A new 458 SOCOM upper and you’re good to go. [See our article comparing 458 SOCOM vs 50 Beowulf here!]

.50 Beowulf

Designed by the legendary Bill Alexander of Alexander Arms, .50 Beowulf / 12.7x42 is yet another thumper cartridge designed to give you a lot of power at short ranges.

While ballistics really aren’t any difference between the big three thumpers, if you want a true 50 cal -- this is the one to get.

[See our complete guide to 50 Beowulf here!]

.300 Blackout

Built for suppressor use and to mimic the ballistics of 7.62x39 while being far more reliable and durable in an AR-15, .300 Blackout is great for things like wild boar.

Because it was designed for short barrels and suppressors, this is perfect for barrels as short as 9-inches. And since subsonic rounds are limited on speed, even in a 9” barrel they give you the same performance.

If you need more punch, load up the supersonics and go to town. [Read our complete guide to 300 Blackout here!]

.300 Ham’r

Introduced a few years ago by Wilson Combat, the .300 Ham’r is actually a pretty reasonable and capable cartridge.

Effectively having the same ballistics as .30-30 (135gr at 2,400 with a 16” barrel) this is a cool addition to the AR-15 lineup.

Sadly, it really isn’t popular… and there is a good reason. Wilson Combat is keeping the cartridge exclusive and proprietary. They are the sole source of parts, uppers, rifles, and ammo.

Hunting Small Game / Varmits

.25-45 Sharps

While some states ban bottle-neck cartridges for big game, still others ban anything at or under .224 caliber.

The .25-45 Sharps set out to make the AR-15 legally viable as a hunting rifle in all states that allowed bottle-neck cartridges by introducing a .25 cal bullet.

Ballistics are solid and are perfectly reasonable for both big game like deer and smaller varments, depending on the bullet you pick.

But this just never caught on. No major brand offers ammo for it and finding a barrel for it is basically impossible.

Using a .223 Remington case that is just opened up to .25 cal, this is very easy to handload if you’re willing to do it.

.22 Nosler

Based on the 6.8 SPC but necked down to .224, the .22 Nosler sends a 55gr bullet at a screaming 3,300 FPS.

And since it uses the same bolt as a normal AR-15, just switching the barrel and using 6.8 SPC magazines makes this a very easy conversion.

But the bad news is that Nosler is the only one offering ammo for it. Their ammo is awesome, but one source isn’t great.

.204 Ruger

An outstanding varmint cartridge, this little guy sends a 32gr bullet at well over 4,000 FPS.

But as you may have guessed, ammo and complete rifles are hard to find. That said, barrels aren’t totally unseen in the wild and building your own upper is pretty easy.

Load up some barrel burners and you can lay out dozens of little critters with ease.

Long Range

.224 Valkyrie

Valkyrie was one of the first “long range” cartridges I ever got into and I really liked it… when it worked.

Sadly, this cartridge was over-promised and under-delivered. While its long range ballistics are very good, there were a number of design issues when it first came out that took time for the community to resolve.

While I ditched it back then after it not performing up to my expectations, the cartridge has found it’s legs and is making a comeback.

Get yourself the right twist and some good loads and you can reach out very far with this little guy.

Plus, it has one of the best names. And yes, that counts.

6.5 Grendel

One of my favorite cartridges, the 6.5 Grendel comes from the mind of Bill Alexander (same guy that made the 50 Beowulf) and is one of the greatest all-round AR-15 cartridges ever made.

Supersonic past 1,000 yards, delivering 1,000 ft.lbf out to at least 400 yards, and still fits 25 rounds in a standard 30-round 5.56 NATO magazine size, Grendel can do a lot of things and do them well.

About the only thing I wouldn’t recommend it for would be really big game, like elk+. Anything else in North America, Grendel can handle it.

It’s also just a really fun round to take long range. Shooting an AR to 1,000+ yards isn’t easy but it is a lot of fun!

[Read our Guide to 6.5 Grendel and find 6.5 Grendel uppers from Bear Creek Arsenal!]

6.8 SPC

Designed in the early 00s in a joint venture between Remington and the Army Marksmanship Unit, this was intended to possibly replace the 5.56 NATO for the US armed forces.

You might have guessed though, it didn’t. While it saw combat overseas with some special forces units (and some claim are still in their inventory to this day) and proved popular with those that put it to the test, it simply didn’t catch on.

Even when something is better than what the military currently uses, sometimes it just isn’t better enough.

Today, the 6.8 SPC is a bit overshadowed by things like 6.5 Grendel, 6mm ARC, and even .224 Valkyrie.

6.8 SPC is good, but might be a second runner-up at best.

6mm ARC

There isn’t much info out about the history of this brand-new cartridge, but what we do know is pretty cool.

Developed by Hornady while working with the DOD, this was designed for an unknown group or agency within the DOD for use in unknown places doing unknown things.

I’m not being cryptic, that is literally all the press release said.

Basically, someone in the DOD wanted a rifle cartridge for the standard AR-15 (or more likely something like the Mk12) that could reach out a lot further with more punch than what 5.56 can do, even the super customized 5.56 that is in use with things like the Mk12.

What Hornady came up with was a 6mm AR-15 cartridge that can sling a 103-grain ELD-X bullet at 2,800 FPS.

That’s pretty darn good for an AR-15. It basically makes it like 6.5 Grendel that ate its spinach.

Parting Shots

That’s a big list, I hope at least a few of them were ones you’ve never heard of!

[As you can see, one of the best things about the AR-15 platform is that all of these calibers (and more) can be fired from a mil-spec AR-15 lower. To add one of these calibers to your arsenal take a look through our AR-15 uppers. These complete upper assemblies come with everything you need to start shooting out of the box including a bolt carrier group and charging handle.]

If your #1 fav cartridge didn’t make the list, let us know in the comments!