8.6 Blackout, By the Numbers
8.6 Blackout was designed by Kevin Brittingham at Q to do for the large-frame AR and short-action bolt gun what 300 Blackout did for the AR-15: shoot heavy subsonic bullets quietly through a suppressor from a short barrel, and switch to supersonics without changing anything but the magazine. It is a shortened 6.5 Creedmoor case necked up to .338, chosen over a shortened .308 because the Creedmoor case is a little more efficient, and it keeps the .308-family case head so it runs on a standard .308 bolt and magazines. The cartridge was designed around a 12″ barrel, which is why the 12″ MATCH-X Gunner exists, with a 16″ for shooters who want a non-NFA rifle and more supersonic velocity.
The twist is the story. Q’s testing found that spinning a bullet faster dramatically increased its terminal effect: going from a conventional twist to 1:7 doubled the initial wound cavity, and going to 1:3 tripled it, while 1:2 started separating bullets in flight. So 8.6 BLK was designed around a 1:3 twist, the fastest in any production rifle, which also gives a 285 to 342 gr subsonic bullet enough spin to stabilize and expand at 1,000 fps. Supersonic 160 to 210 gr loads run about 1,950 fps from a 12″ barrel.
8.6 Blackout is now SAAMI-standardized, at a 1:6 twist rather than the original 1:3. Faxon makes 8.6 BLK barrels to both specifications. The MATCH-X barrels on this page are the original-spec 1:3, so use ammunition loaded for a 1:3 twist; loads developed for the 1:6 SAAMI twist may not perform as intended in them. Faxon has also seen inconsistent 8.6 BLK ammunition on the market; these barrels are chambered and headspaced to the cartridge print, and ammunition that does not match it cannot be guaranteed to chamber, cycle, or extract.
Representative factory loads (maker-published)
| Load | Type | Velocity | Energy |
| Gorilla 210 gr Barnes TSX | Supersonic | 1,950–1,970 fps (12″) | ~1,800 ft-lb |
| Gorilla 342 gr Pork Shredder | Subsonic | ~1,000 fps | ~700 ft-lb |
| Hornady 315 gr Sub-X (component / factory) | Subsonic | ~1,000 fps | ~700 ft-lb |
Sources: maker-published figures collected by Ammo.com and Outdoor Life (Q’s 12″ data). Hornady does not publish an 8.6 BLK factory table. Subsonic performance is essentially identical from the 12″ and 16″ MATCH-X barrels; supersonics gain roughly 100–150 fps in the 16″. Confirm every load is intended for a 1:3 twist.
What You Need to Build It
DPMS / LR-308-pattern upper and barrel nut, a standard .308 bolt carrier group, and SR-25 / DPMS-pattern magazines. .875″ gas block; a pistol-length gas tube for the 12″ and a carbine-length tube for the 16″. M18x1.5 muzzle with the 8.6 taper shoulder; a taper adapter ships with every barrel. Headspaced with an 8.6 BLK go/no-go gauge.
What Every MATCH-X Barrel Shares
416-R stainless bar stock, drilled, reamed to 32 Ra, honed to 8 Ra before the rifling button goes through, 5R button rifled, stress relieved at 1150°F, contoured, chambered, then lapped back to a uniform 16 Ra from throat to crown. Bore and groove air-gauged at three points, honed finish read on a profilometer, borescoped, chamber verified on a CMM, magnetic-particle inspected, nickel-Teflon extension torqued to 150 ft-lb, pinned, and headspaced. Exterior left as bare stainless blasted with S110 media. Made in Greater Cincinnati, Ohio, backed by the Faxon Lifetime Guarantee. See the whole MATCH-X line and the process video ›
MATCH-X 8.6 Blackout FAQs
Should I choose a 1:3 or a 1:6 twist 8.6 BLK barrel?
Match the barrel to the ammunition. 1:3 is the twist the cartridge was designed around and what the original and most heavy subsonic loads are built for; 1:6 is the SAAMI-standard twist and what SAAMI-spec ammunition is developed for. Faxon makes both. These MATCH-X barrels are 1:3; buy ammunition that states it is loaded for a 1:3 twist.
12 or 16 inches?
12″ is the length 8.6 BLK was designed around; subsonics give up nothing to the 16″, and it makes the shortest suppressed large-frame gun there is. The 16″ adds roughly 100 to 150 fps on supersonics and keeps a rifle non-NFA with a fixed stock.
What is the tapered muzzle and the included adapter?
The muzzle carries M18x1.5 threads behind the 8.6 Blackout taper shoulder, the mounting standard the cartridge was introduced with, which lets a taper-mount suppressor index on the taper for repeatable alignment. A taper adapter ships with every barrel so you are not limited to taper-mount devices. The 8.6 barrels carry no caliber rings; the taper is the identifier.
Which gas block does it take?
A .875″ gas block on a 1.9″ journal, and Faxon recommends its .875″ adjustable block: nearly every 8.6 BLK build runs suppressed and switches between subsonic and supersonic loads, and the block's gas tube seat sits .080″ higher than its smaller blocks so the tube clears the barrel nut on a short AR-10 gas system.
