Lesser Known AR-15 Calibers

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The AR 15, first developed by Eugene Stoner over half a century ago, has become one of the most widely
adopted and successful firearms in modern history. Most of the time, we see it in its standard
chambering, .223 or 5.56mm NATO. But, over the long and storied history of the AR platform, there
have been a lot of interesting calibers that have been tried.

For each of these unusual calibers, we’ll start by briefly introducing it and giving some of the reasons
behind its development. From there, we’ll talk about intended uses for some of these, which can get
both interesting and highly specific.

.50 Beowulf
.50 Beowulf is, as the name implies, a .50 caliber round for the AR platform. To shoot this 12mm
behemoth, you’ll need a whole new upper receiver, as is common with these unusual calibers, but, it
uses standard AR magazines.
The 50 Beowulf is a .50 caliber round, yes, but it’s a short one, using the same overall length as standard
5.55mm NATO. As far as intention goes, this is a special tool meant to stop vehicles that refuse to stop
at checkpoints. It was first developed and saw limited adoption in Iraq and Afghanistan in the US’
involvement in both nations increased with the Global War on Terror.

.300 Blackout
A relative newcomer to the scene, the .300 Blackout has become one of the most popular AR cartridges
of the last several years. It was developed in response to a more or less perennial search since the
adoption of the M16 in the 1960s for a larger caliber version that would suppress well.
The .300 blackout does just that, working spectacularly well with subsonic rounds and making for a
suppressed AR package that leaves the 5.56mm in the dust in terms of noise reduction.

While it’s coming back now into fashion with the concept of a pistol caliber carbine, there have been
9mm ARs since the very beginning. Known as the AR9 in some circles or as the Colt SMG635 in others,
folks have been using ARs in 9mm since the 1960s.

The main benefit to a 9mm AR, usually, is its compact size when compared to a standard M16, especially
in the era when 20” barreled guns were the norm. Thus, tankers, aircrews, drivers, and some people on
executive protection details have gone with 9mm ARs over the years.
One of the big critiques of the 5.56mm is that it often takes more than one round to end the threat
posed by an enemy combatant. While this was well known by the end of Vietnam, it took Operation
Gothic Serpent, also more commonly known as Blackhawk Down, to get the Army’s attention.

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In an attempt to make an AR that would do better at short to medium range antipersonnel work, the
Army, especially Task Force Ranger, encouraged the development of .458 SOCOM which is a nearly .50
caliber round that is meant specifically for missions like Black Hawk Down. It’s uncommon to see now,
but if you need a bullet that hits like a freight train, this is the one for you.

.22 Long Rifle
There have been ARs made in .22 long rifle for some time now. While a lot of folks write them off as
novelties or toys, at a time when 5.56mm is outrageously expensive, being able to shoot an AR of any
kind for a reasonable price is a good training tool in my book. Nowadays, most manufacturers make an
AR in 22, and it can be an excellent way to train or to get new folks into the AR world without
developing a flinch.

7.62×51 NATO
Here I’d also like to five 7.62mm NATO an honorable mention. Technically, it’s not an AR15 caliber: it’s
an AR10 caliber. This distinction only matters if we’re talking in terms of history. Originally, Eugene
Stoner developed the AR10 for the same rifle trials in which the US would ultimately adopt the M14, and
it did see some limited commercial success, for example, in Angola, Cuba, and Portugal. The US would
choose to adopt the M14, an overall heavier, less reliable gun, and ask Stoner to draw up something
new, the AR15 years later.

As you can tell, the AR comes in a massive range of calibers, and we’ve only touched on a few of them
here. This is, I think, a testament to Stoner’s great designs: it’s uncommon to have a single type of action
get such widespread use, from range plinkers in .22 all the way up to .50 caliber vehicle stoppers. If
there’s some shooting that you need to do, there’s a high chance that someone, somewhere has made
an AR specifically for the task. Whatever caliber you have, though, it’s never a bad day at the range as
far as we’re concerned.