The 8.6 Blackout: New King of the Subsonic Cartridges?

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I love the .300 Blackout. I’ve used it to shoot steel, hunt big game,and I trust it for self-defense. The engineering minds behind the .300 Blackout have created a more powerful cartridge called the 8.6 Blackout (BLK). This cartridge was created by Kevin Brittingham and his team at Q. The 8.6 applies the .300 BLK’s design principles to the larger and further reaching AR-10 platform. The 8.6 BLK brings new levels of energy and distance to the subsonic game, and its bullets can take down some of the largest, toughest animals on the planet.

Think of the 8.6 BLK as the .300 BLK’s big brother. It has twice the reach, produces double the energy, and triples its lethality. All that’s required to convert an AR-10 or .308 Winchester-sized bolt gun to 8.6 BLK is a simple barrel swap. It’s a dual-purpose cartridge that shoots .338-caliber bullets in the 160- to 210-grain range at supersonic speeds and 280- to 350-grain bullets at subsonic velocities. The 8.6 BLK excels in short, light guns that are handy in the field and quick on target. The 8.6 BLK is based on a shortened and necked up 6.5 Creedmoor case to facilitate correct seating and feeding of the long, high-ballistic-coefficient bullets that provide maximum subsonic power from a .308-sized platform. The 8.6 BLK utilizes a 30-degree shoulder for a compact, consistent powder burn.

The 8.6 BLK employs a radical 1:3-inch twist. This fast twist achieves fantastic accuracy with the 8.6’s heavy, subsonic bullets. This twist rate is so fast that non-bonded bullets will come apart at the muzzle at supersonic speeds, so solid copper or bonded bullets are required. All current Barnes hunting bullets function with the twist. Bullets spinning over 500,000 rpm are devastating to targets. Brittingham describes it as turning up your blender setting from slow grind to max liquify. It’s so intense that the copper petals on monolithic bullets not only peel straight back but twist as well. Wound channels in ballistic gelatin and on game are three times as large as the channels made by more traditional twist rates. The 1:3-inch twist also facilitates reliable expansion at lower velocities. To convert any AR-10 or .308-based bolt gun to 8.6 BLK, a simple barrel swap is all that’s required. With the Creedmoor as the parent case, the 8.6 uses a standard bolt and feeds and functions at full magazine capacity from AR-10/SR-25/AICS-pattern magazines without modification. An interesting observation is that the outside neck measurement of a loaded .308 Winchester round measures .338 inches. The 8.6’s .338 bullet fills that same space in the magazine for a perfect fit and reliable feeding.

How Does 8.6 Blackout Perform?

The 8.6 fires supersonic bullets in the 160- to 210-grain range at 2,000 to 2,400 fps respectively. Subsonic bullets from 286 to 350 grains are fired just under the sound barrier at around 1,050 fps. For comparison, .300 BLK uses 110- to 150-grain supersonic bullets, with subsonics weighing around 200. Bullets designed specifically for the 8.6 BLK are pushing the boundaries of performance and crossing into a new horizon of subsonic lethality. Because the projectiles must stay under the sound barrier, the only way to increase energy is to increase bullet weight. A 350-grain subsonic bullet in the 8.6 BLK produces around 830 ft-lbs of energy compared to the .300 BLK’s 200-grain bullets that produce only 490. Supersonic energy for the 160- to 210-grain 8.6 BLK bullets will be around 1,800 to 2,000 ft-lbs. The 8.6 maximizes bullet weight and geometry with bullets that will still feed reliably in a standard AR-10 or bolt-action platform.

With supersonic bullets, the 8.6 BLK is a legitimate 450-yard hunting cartridge. This is a huge gain over the .300 BLK that maxes out at about 200 yards. With subsonic loads in the 8.6, one can be confident to beyond 300 yards. The fast twist increases the reliability of bullet expansion at longer distances. For this article, I drove to Sundance, Wyoming, to meet with David Stark, the owner of Discreet Ballistics. Stark is at the forefront of 8.6 BLK ammo production and technologies. We tested his Hotline Munitions 185-grain Hornady CX supersonic load through my 8.6 build. The all-copper bullet is deadly on game and shot a 1-inch, three-shot group at 100 yards. His Discreet Ballistics 300-grain FMJ subsonic load was soft shooting, accurate, and smacked the steel hard. I fired several tight groups with it at 50 yards where supersonic and subsonic trajectories are on similar points of impact. I was also able to test these loads through Q’s The Fix bolt-action rifle with deadly results.

So, who designed the 8.6 BLK? That would be Kevin Brittingham and the team at Q. They began production on the 8.6 BLK in 2018, but manufacturing and supply chains got derailed by COVID. The 8.6 BLK is now gaining strength and momentum across the shooting community. It’s such a smart, simple, and effective design that it will have a bright future. Is the 8.6 BLK for you? If you’re after a deadly hunting cartridge at subsonic and supersonic speeds, then yes, there is no arguing the results of a 210-grain supersonic or 340-grain subsonic copper bullet churning through flesh. Brittingham has used it to take down Cape buffalo and other tough animals in Africa. The Department of Defense is attracted to its extended subsonic capabilities for obvious reasons. I built mine to hunt elk and deer and use for self-defense.

Firearms and Parts for the 8.6 Blackout

Faxon Firearms is leading the way for 8.6 BLK AR-10 guns and parts. They sent me a 12-inch barrel, 10-inch handguard, .875-inch gas block, and a three-chamber muzzlebrake. I built a handy gun that is great to carry in the woods, feeds flawlessly, and will put down animals with authority. Q chambers the 8.6 BLK in The Fix rifle. More manufacturers are building guns and parts every day. Ammunition is the bottleneck right now but becoming more available. Discreet Ballistics is full steam ahead with production. Their 286-grain monometal load is deadly for all tasks from self-defense to hunting. Hornady worked with Q on designing and measuring pressures for the 8.6 BLK and is producing reloading dies and brass. While 6.5 Creedmoor brass can be formed into 8.6 BLK brass by the ambitious reloader, it is a tedious process. During testing, I shot Q’s 8.6 BLK specific suppressor called the Pork Chop. It’s designed to be short and lightweight for hiking in the woods and makes suppressed loads sound quieter than a .22. SilencerCo also offers their .338-caliber Harvester suppressor. Suppressors for 9mm and .45-70 will work, just not as effectively as a .338-specific can. But a suppressor isn’t required to reap many of the benefits of shooting the 8.6, as the large bore and efficient powder charge make for mild blast and pleasant shooting.

Conclusions on the 8.6 Blackout

The innovation, collaboration, engineering, and manufacturing behind the 8.6 BLK is impressive. As the .300 BLK’s big brother, the 8.6 BLK is a welcome addition that adds significant power and reach to supersonic as well as subsonic shooters. Millions of rounds of ammunition are in the production queue, and dozens of companies are starting to crank out firearms, ammunition, and parts. Long live the 8.6 BLK!

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