300 Blackout (BLK) - The Hipster Caliber?

300 BLK, a hipster caliber?

If you are new to the world of firearms, you might think that an AR-15 can only chamber and fire .223 caliber and 5.56mm ammunition. Out of the box, you would be correct. Most of the copies of America’s Favorite Rifle run that caliber of ammunition. However, changing the caliber you can fire is as easy as swapping the upper. There are many alternative calibers for the AR available, including 300 Blackout, aka 300 BLK.

A Little History On 300 Blackout (300 BLK)

The most widespread cartridge for the AR/M16/M4 type of rifle is, of course, the 5.56mm NATO. Developed in the 1960s as an intermediate cartridge, the rage back in those days was for lighter and smaller projectiles that derived their power from sheer velocity. Paired with a then-standard 20-inch barrel on an AR-15 or M16, the 5.56mm whizzed along at 3025 feet per second, which works out to over 2000 miles per hour. The idea was that a user could carry more ammunition since the rounds were smaller and lighter than the bigger .30 caliber service rounds like .308 and 7.62 x 51mm.

The tradeoff, of course, was barrel length. To get that round up to where it needs to be in terms of speed, a lengthy barrel was required. As the military shifted it’s missions in the 1960s to engagments in jungles and urban areas, a large rifle became a liability. So, the 5.56mm started to exhibit performance issues out of shorter-barrel weapons. Plus, it was loud for it’s size and suppression proved initially problematic. Other cartridges were proposed for military use, but each required essentially a new firearm platform to be developed. Colt, Armalite, and the military had just invested tons of money in the AR-15/M16, and weren’t in the mood to pivot to yet another rifle platfom. So with incremental bullet design improvements, 5.56mm remained, and still remains the military and citizen standard for the AR platform. However, there’s always been a push to step up to a different cartridge, usually in the .30 caliber class. Many cartridge designs were proposed and tested, but bothe the citizen and military world stuck with 5.56mm-chambered ARs.

Simply put, because there’s a huge installed base of firearms, magazines, and components. Proposed successors to the 5.56mm usually required new bolt carrier groups, new magazines, or even entire new weapons platforms. Getting new guns out there, especially to government agencies, which aren’t known for speed, would be a near-impossible task. Even when conversions to bigger cartridges were somehow magically coaxed into the AR platform, problems arose. Just ask anyone who has tried to build a 7.62x39mm (AK ammunition) AR.

Enter 300 Blackout.

The Advantages Of 300 Blackout

Developed by Kevin Brittingham (now of Q fame) and his original company Advanced Armament Corporation, 300 BLK was specifically designed to not only perform well out of a shorter-barrel rifle while suppressed, but also require a minimal amount of modification to the host platform, in this case the AR/M4. Derived from the “wildcat” 300 Whisper cartridge (in ammo-nerd-speak, a “wildcat” cartridge is one that isn’t standardized and often custom made for one specific gun), the 300 BLK fit the bill. All that was required to convert a standard AR or M4 was a barrel swap. Existing standard capacity magazines could be used to their full 30 rounds, and existing bolt carrier groups could be used. Converting an AR could easily be done by anyone with a modicum of gunsmithing knowledge, or none at all, as a complete upper could be shipped to the end user, which can be changed in less than a minute.

Furthermore, the ammo could cycle and run effectively in an AR in both subsonic and supersonic varieties. For suppressor users, subsonic ammunition is of importance since it negates the sonic boom as the projectile breaks the sound barrier. Yes, this means the projectile itself is traveling at around a third of the velocity of the 5.56mm round, but the heavier subsonic projectiles impart more damage upon impact than a lighter round traveling at the same velocity. Even the supersonic rounds suppress well, utilizing less powder to propel the projectile at an effective velocity as compared to 5.56mm.

For reloaders, 300 BLK is a viable alternative AR caliber since they can trim down existing 5.56mm brass to accomodate the .30 caliber projectile of their choice.

The Disadvantages of 300 Blackout

Much like any other cartridge, the 300 BLK isn’t a “do everything well” cartridge. There are noted disadvantages to the cartridge.

One, simply is cost. 5.56mm is cheap since there’s a huge installed base of users, and nearly 60 years of continued production. The machinery is out there, tested, and working non-stop to produce ammunition for professional and citizen use. This has driven down the price of 5.56mm enormously, with ammunition being below $0.20 per round in some cases. 300 BLK? It’s a rare find to see it below $0.60 a round. Subsonic match loads often cost more than $1.00 per round. A full-auto magazine dump of subsonic 300 BLK is literally turning money into noise.



In the above video from a few years ago, we used 220-grain 300 BLK loads from Norma Ammunition at $1.30 per round. In less than ten seconds, I shot nearly $40 worth of ammo downrange. Fun, but pricey. Even supersonic loads are expensive. 300 BLK is still a boutique, hipster caliber. Sure, some secret squirrel units around the world have adopted it, but it hasn’t been enough to flood the supply chain yet and drive costs down.

Another disadvantage is a little more nefarious. Since 300 BLK is designed for maximum compatibility with the standard AR platform, a 300 BLK round will load into a 5.56mm-chambered AR, resulting in what we call a “ka-boom”. The projectile has nowhere to go, and thus plugs the barrel. The firing pin will engage the primer since it’s in the same spot as a 5.56mm load. The pressure has to go somewhere. At the very least, you’ll wreck your upper. If you’re using cheap components, you could very well get a face full of shrapnel. If you’re a 300 BLK shooter, do yourself a favor and keep everything super-segregated. Don’t even bring a 300 BLK gun with you to the range on a day you’re shooting 5.56. Another tip is to notate your magazines and even use dedicated 300 BLK magazines such as the 300 BLK-dedicated magazine from Magpul. It’s actually pretty neat, it’s super-optimized for the load and negates the occasional malfunction 5.56mm magazines present to the cartidge.

A third disadvantage is, of course, usage. Someone who has used 5.56mm for decades has to readjust their thinking for a different caliber. Optics have to be re-zeroed, and so forth. It can be overcome, but sheer human inertia presents a challenge to the adoption of the round.

300 BLK Is Here To Stay

It’s been 11 years since 300 BLK made it’s debut on the world stage. It’s hung around as the “hipster” caliber of the AR world. Expensive, bespoke, and appealing to a small subset of gun owners. But I think it’s attained a small self-sustaining reaction, in part due to it’s friendly compatibility with the existing AR platform. This year, major manufacturers such as Daniel Defense are dropping complete 300 BLK firearms explicitly targeted to the home and citizen defense market.

Plus, there’s a small universe of 300 BLK ammunition.

RoundCostBuy Now
Hornady 220gr Sub-X$24.00Buy Now!
Hornady 110gr BLACK$21.00Buy Now!
Federal 150gr PowerShok$20.00Buy Now!
Sellier & Bellot 200gr Subsonic Bulk$285.00Buy Now!

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