8.6 Blackout: Barrels, Rifles & Suppressors
Built for Subsonic Dominance

8.6 Blackout (8.6 BLK) is a .338-caliber rifle cartridge designed for suppressed subsonic use. Developed by Q LLC and Kevin Brittingham, it uses modified 6.5 Creedmoor brass necked up to .338 caliber, fires 210–300+ grain bullets, and operates on standard .308 bolt-face AR10 or bolt-action platforms. At subsonic velocities, the combination of large bore diameter, heavy bullets, and fast 1:3 twist rate creates devastating terminal performance that far exceeds what 300 Blackout achieves at similar velocities.

The original 8.6 BLK specification requires a fast 1:3 twist rate. This is not a typo — one rotation every 3 inches is intentional. The extreme spin maximizes terminal performance at subsonic velocities by causing heavy bullets to yaw and fragment aggressively upon impact, creating wound channels far beyond what a slower-twist barrel would produce. Faxon also offers 1:6 twist barrels in the newer 8.6 BLK SAAMI specification for shooters who prefer the SAAMI-standardized variant or a slightly slower twist for broader bullet weight compatibility.

Yes — that's exactly what it was designed for. 8.6 BLK uses the standard .308 bolt face, so any AR10 chambered in .308 Win or 6.5 Creedmoor can be converted to 8.6 BLK with a barrel swap. You'll need an 8.6 BLK-chambered barrel with the correct 1:3 or 1:6 twist, and your standard .308 bolt and .308 magazines will work. No lower modifications required.

For suppressed subsonic use, 8" and 12" barrels are the most popular choices. 8.6 BLK subsonic loads are intentionally loaded below 1,050 fps, and short barrels don't sacrifice meaningful velocity on already-subsonic loads — they just reduce the overall suppressed system length. A 12" barrel gives a good balance of reduced length and complete powder burn. A 16" barrel is better for supersonic loads, general-purpose use, or where suppressor isn't being used.

You need a suppressor rated for .338 caliber or larger. Faxon's Harmonix® Sentry, Harmonix® ION, Harmonix® Ti•CONEL, CoreSync®, and Basilisk® suppressors are all rated for .36 caliber (9.1mm bore), which covers the .338 bore of 8.6 BLK. Faxon barrels are threaded M18×1.5, compatible with Faxon's MuzzLok® direct-thread and Plan B quick-attach mounting systems.

The original 8.6 BLK uses a 1:3 twist rate and is the proprietary specification developed by Q LLC. 8.6 BLK SAAMI is the Sporting Arms and Ammunition Manufacturers' Institute standardized version, using a 1:6 twist rate. SAAMI standardization means more ammunition manufacturers can produce 8.6 BLK SAAMI ammo to a common spec, potentially increasing availability over time. The 1:3 twist (original) provides the most aggressive terminal performance with heavy subsonic bullets. Both are available in Faxon's barrel lineup.

8.6 BLK significantly outperforms 300 Blackout in terminal effectiveness at subsonic velocities. The larger .338 bore (vs .308), heavier projectiles (210–300+ gr vs 200–220 gr), and 1:3 twist-induced fragmentation create dramatically larger wound channels. 300 BLK runs on the lighter AR15 platform; 8.6 BLK runs on the larger AR10. 8.6 BLK is more powerful and terminally superior but in a heavier, larger system. If you already own an AR10, 8.6 BLK is a straightforward barrel swap upgrade with significant performance gains over 300 BLK at subsonic velocities.

Yes. All Faxon barrels are manufactured at our facility in Greater Cincinnati, Ohio. Faxon Machining has been precision machining since 1978 — originally serving automotive, oil & gas, aerospace, and defense industries before Faxon Firearms was founded in 2012. Every barrel starts from certified bar stock steel, is drilled and reamed in-house, button-rifled, stress-relieved in our ovens, air-gauged for bore consistency, Magnetic Particle Inspected (MPI), and measured on our CMM and Marshaft equipment. We are ISO 9001:2015 certified.

Faxon offers a Lifetime Guarantee on our barrels. If your Faxon barrel develops a defect in materials or workmanship, we will repair or replace it. This covers our entire 8.6 BLK barrel lineup — Duty, Match, Match-X, FX7 Prefit, Remage, and Savage 110 series.

8.6 BLK uses standard .308/SR25-pattern AR10 magazines. The cartridge headspaces on a standard .308 bolt face and feeds from .308-format magazines — the same magazines used with .308 Win and 6.5 Creedmoor AR10 builds. No proprietary magazines are required.

Yes — 8.6 BLK is increasingly popular for hog hunting, deer, and predator hunting, particularly when suppressed. The 1:3 twist-induced fragmentation at subsonic velocities creates exceptional terminal performance on medium game at ranges up to 150–200 yards. For larger game at longer ranges, supersonic loads with lighter bullets (150–180 gr) extend effective range. The suppressed bolt-action configuration (FX7 + Faxon Harmonix) is especially popular for quiet, night-vision-compatible hog hunting.