300 Blackout: Why It's One of The Best AR-15 Cartridges

Thew AR-15 chambers a lot of popular cartridges. But 300 Blackout remains one of the top contenders for those looking to move away from "boring old" 5.56 NATO and .223 Remington. Let's review why 300 BLK is, indeed, arguably one of the best overall AR-15 rounds today.

What is 300 Blackout?

Officially called 300 AAC Blackout (designated 300 BLK by SAAMI standards), this 7.62x35mm cartridge was developed by Advanced Armament Corp (AAC) specifically to replace the 5.56 NATO cartridge used by the U.S. military.

Robert Silvers, the director of research at AAC, said:

"We started development in 2009, but most of the work was done in 2010. A military customer wanted a way to be able to shoot .30-caliber bullets from an M4 platform while using normal bolts and magazines, and without losing the full 30-round capacity of standard magazines. 

They also wanted a source for ammunition made to their specs. We could not have just used .300-.221 or .300 Whisper because Remington is a SAAMI company, and will only load ammunition that is a SAAMI-standard cartridge. We had to take the .300-221 wildcat concept, determine the final specs for it, and submit it to SAAMI. We did that, and called it the 300 AAC Blackout (300 BLK)."

Why You Should Pick 300 Blackout

The round was approved by SAAMI on January 17, 2011. Later that year, Army Staff Sergeant Daniel Horner used the round to win his fourth USPSA Multi-Gun National Championship. Since then, 300 Blackout has become perhaps the second most popular cartridge (next to 5.56 NATO and .223 Remington) chambered in the AR platform. But why? Let's review.

The Best Subsonic Performance

The single most effective way to "quiet down" the AR-15 is by chambering 300 Blackout. This writer can attest to its subsonic, suppressed performance, having built a few 300 BLK ARs, and having tested out various .30-caliber suppressors to muzzle the round.

The suppressed 300 Blackout can be made quieter than even the sound of the action itself cycling. It can be made quiet enough for shooting indoors with no hearing protection -- and it does all this without needing to extensively modify the AR-15 to handle these low-power loads. 

300 Blackout was, in fact, designed to be capable of firing supersonic and subsonic with a suppressor without changing the gas system, recoil spring, or buffer weight. There are currently no other cartridges available for the AR platform that can do the same.

The Broadest Suppressor Compatibility

For a particular cartridge to enjoy such a high level of suppressed performance, suppressor makers have to cater to it. Thankfully, 300 Blackout has found itself in a positive feedback loop, here: 

The round's popularity has made suppressor manufacturers develop plenty of 300 Blackout-specific models, which has caused more and more AR owners to adopt the cartridge. The more owners adopt the round, the more the suppressor market caters to it.

At the time of this guide's publication, suppressors marketed for .30-caliber rounds -- many of which specifically advertise being optimized for 300 Blackout -- remain the most popular, affordable, and widely available models through dealers, with hundreds of options currently in production.

Parts Compatibility (Easy Conversion!)

Own a regular 5.56 NATO- or .223 Remington-chambered AR-15? Want to switch to 300 Blackout? Converting your AR is incredibly easy. In fact, if you have a "standard" AR-15 a Carbine buffer, you only need to swap the barrel and gas system.

Besides the barrel and gas tube length, all other parts in the upper and lower receivers, including bolt, lower parts kit, and the receivers themselves, are reused when building an AR-15 that chambers 300 Blackout.

Many AR owners simply buy a barreled upper assembly, throw it on their existing lower, and they're ready to swap their magazines from 5.56 or .223 to 300 BLK.

Shop 300 Blackout uppers here!

More Power in a Smaller Package

In its supersonic form, 300 Blackout round provides more knockdown power than 5.56 NATO and .223 Remington. By using a standard .30-caliber bullet, the round can also provide significantly better ballistic coefficients, resulting in substantially more velocity and energy retention downrange. This all translates into more lethality at up to 300 to 400 yards.

Advanced Armament Corp. also designed 300 Blackout to produce optimal velocity and performance in short barrels -- you no longer need a 16" to 20" barrel (like you would with 5.56 and .223) to maximize effective range. AAC says 300 Blackout high power and long-range accuracy with a barrel just 9" to 10" in length.

Shorter setups can still provide more than adequate knockdown power, too. Popular 300 BLK-chambered AR models designed specifically for short-range, suppressed fire, like the Q Honey Badger and Sig Sauer Rattler, use barrels as short as 7" and 5.5", respectively.

Shop 300 Blackout AR Pistol kits here!

The AR's Most Affordable Alternative Cartridge

Gun owners love the AR-15 because it's an affordable platform. Its 5.56 and .223 ammo is some of the cheapest rifle ammo for sale today, with a cost per round as low as $0.65. 

While most other rifle rounds for sale today average well over $1.00 per round, 300 Blackout remains the notable exception. At the time of this publication, subsonic 300 BLK ammo costs as low as $0.75 per round. Supersonic ammo's even cheaper, with options as low as $0.50 per round.