FAXON DUTY SERIES GUNNER PROFILE 12" 1:3T PISTOL-LENGTH 8.6 BLK AR10 BARREL

Rifle Barrels › Duty Series › 8.6 BLK › 12″ Gunner, Pistol-Length  |  Works with: .308-family BCG • .875″ gas block • pistol-length gas tube • M18x1.5 muzzle devices • .36 cal suppressors

Why 8.6 Blackout, Why 12″, and Why the Gunner Profile

8.6 Blackout is what 300 Blackout would be if it were designed around a .338 bullet and an AR-10: a .308 case shortened and necked up, so it runs in a standard AR-10 upper with a .308 bolt face and .308 magazines, and built to be shot suppressed and subsonic. The trick is the twist. A 1:3 barrel spins a 300 gr bullet at roughly 240,000 rpm at 1,000 fps, and that rotational energy is what makes it yaw and fragment in game or gel at velocities where a conventional-twist bullet would pass through. Faxon was the first company to button-rifle 1:3 twist 8.6 BLK barrels in production. Supersonic 150 to 180 gr loads make it a 200-yard hog and deer cartridge with the block turned up; subsonic 210 to 300-plus gr loads make it the quietest centerfire rifle you can build. Faxon’s 8.6 Blackout guide covers the cartridge, the twist, the ammunition, and the suppressors in detail.

Twelve inches is the length 8.6 BLK was optimized for: the cartridge burns its charge in the first eight or nine inches, so a 12″ gets the full subsonic velocity and almost all of the supersonic velocity a 16″ does, in a pistol or SBR that balances with a can on it. The Gunner profile, which Faxon called the Big Gunner until it simplified its naming in 2026, is the AR-10 version of its most popular contour: a full 1.000″ chamber journal and a .875″ gas journal where the barrel takes its load, then a .753″ section tapering to .723″ ahead of the block where diameter only adds weight, for a .338-bore barrel that weighs 2.0 lb and reviewers describe as heavy for its length in the right way. The muzzle is M18x1.5 with a 20° tapered shoulder, the standard 8.6 BLK thread, so taper-mount suppressor adapters seat on the taper and the HUB adapters and MuzzLok brakes thread on. If the gun is going to live in a bag, the 8″ 8.6 BLK is the shortest package; if it needs a stock and no paperwork, the 16″ carbine-gas 8.6 BLK is the rifle. Faxon builds this barrel into the Sentinel 12″ 8.6 BLK pistol if you would rather have it done.

What “Duty Series” Means

Duty Series is Faxon’s 4150 CMV line: the M4/M16 barrel alloy, salt-bath QPQ nitrided inside and out. 4150 carries about 0.50% carbon plus vanadium, which gives it more strength and wear resistance at temperature than 4140, and nitride adds a hard, corrosion-resistant surface to the bore and exterior without plating anything, and it adds virtually nothing to the surface: a few ten-thousandths of an inch, roughly a tenth the width of a human hair. It is the right combination for a barrel that will be shot hard, carried in the weather, and cleaned when there is time. Faxon’s stainless Match Series is the option when you want the precision-barrel formula; the Duty Series is the one to reach for when the rifle has a job.

What’s in the Box

How It’s Made

Every Duty Series barrel is made start to finish in Faxon’s Greater Cincinnati plant, on Faxon’s machines, to Faxon’s prints. This is the routing for this barrel.

1. Drill and pull-ream 4150 CMV bar is gun-drilled, then pull-reamed from the chamber end to a .3310″ bore held to ±.001″, with a 32 Ra maximum finish checked on a profilometer and a borescope pass for reamer marks.
2. Button rifle A carbide button is pulled through from the chamber end to form five grooves, right-hand, one turn in 3 inches, to a .339″ groove diameter. Bore and groove are air-gauged.
3. Stress relieve and qualify The rifled blank is stress relieved before it becomes a finished barrel, then the OD is qualified true to the bore so every later cut references the same axis.
4. Turn the Gunner profile Muzzle end first: the .875″ gas journal is turned to .8740–.8747″ and checked with a micrometer on every barrel, held within .005″ of the bore, the .753″ to .723″ forward section is turned true to the same axis, and the M18x1.5 muzzle is threaded, its 20° taper cut, and crowned. Then the breech end: the 1.000″ chamber journal and the 1-16 extension thread.
5. Chamber The 8.6 BLK chamber is cut and checked with a headspace gauge; chamber surfaces are held to a 20 Ra finish.
6. MPI and nitride The machined barrel is 100% wet magnetic-particle inspected for surface and near-surface flaws, then salt-bath QPQ nitrided inside the bore and out, hardening the surface while adding virtually nothing to it.
7. Gas port, extension, pin After nitride, the .078″ gas port is drilled and reamed through the .875″ journal, the DPMS-pattern .308 extension is torqued to 150 ft-lb and pinned, and the barrel is headspaced with an 8.6 BLK go/no-go gauge.
8. Mark The Faxon shield and order number are laser-engraved on the chamber journal and “8.6 BLK 1-3T” ahead of the gas block.

What Reviewers and Owners Say

Voted Favorite Aftermarket Barrel by Shooting Sports Retailer every year since 2022 — the Gold Award, the top honor in the category. Faxon also took the Tactical Retailer Gold Award in the same category in 2025. Here is what independent testers and buyers have said about Faxon barrels and this one.

5.0 stars across 6 reviews on FaxonFirearms.com, and 5.0 across 2 at Primary Arms.

Build It Out: Faxon Parts That Fit This Barrel

Everything below is made or specified to the same prints this barrel is, so the gas system, extension, and muzzle line up the first time. Pick one from each row and the upper is done.

Duty Series 12″ Gunner 8.6 BLK FAQs

Is 8.6 BLK a SAAMI cartridge, and what ammunition should I run?

It is now. SAAMI accepted 8.6 Blackout in January 2026 with a 62,000 psi maximum average pressure. This barrel is chambered to the 8.6 BLK cartridge drawing and headspaced with an 8.6 BLK go/no-go gauge after the extension is installed, and it is cut with the 1:3 twist the cartridge was designed around. Faxon has seen ammunition on the market that does not match the cartridge drawing; ammunition loaded to the drawing runs, and ammunition that is not cannot be guaranteed to feed or extract. Check the drawing in Faxon’s 8.6 BLK guide before you buy a case of something new, use the same caution you would with any reloaded ammunition, and if a load will not run, customer service wants to know which one.

Why pistol-length gas on a 12″ 8.6 BLK?

Because 8.6 Blackout is a short-barrel cartridge by design. It burns a fast powder charge behind a heavy bullet, so pressure peaks early and the port has to sit early to catch it: Faxon puts it about 4.8″ from the breech with more than seven inches of barrel past it for dwell. The port is reamed to .078″, small for a .338 bore, because a 300 gr subsonic and a 160 gr supersonic put very different gas through the same hole and the system has to run both. With a standard AR-10 carbine buffer it cycles supersonics unsuppressed and subsonics suppressed; an adjustable .875″ block is how you make one upper do both without swapping buffers. This barrel needs a pistol-length gas tube.

What is the Gunner profile on an AR-10, and what happened to “Big Gunner”?

Same barrel, simpler name: Faxon dropped the “Big” in 2026 so its AR-15 and AR-10 Gunner barrels share one profile name. On an AR-10 it means a full 1.000″ chamber journal and a .875″ gas journal, the AR-10 standard, where the barrel does the most work, then a .753″ section tapering to .723″ toward the muzzle where mass adds weight without adding stiffness. On a 12″ 8.6 BLK it weighs 2.0 lb, enough steel for a .338 bore and a can, without the front-heavy feel of a straight .936″ profile.

Why 1:3 twist, and what bullets does it stabilize?

Because 8.6 BLK is a subsonic cartridge first, and a 300 gr bullet at 1,000 fps has no velocity to do terminal work with. The 1:3 twist spins it at about 240,000 rpm, roughly three times what a conventional twist would, so the bullet arrives with the rotational energy to yaw and fragment on impact instead of pencilling through. That is the whole idea of the cartridge, and Faxon was the first company to button-rifle a 1:3 twist 8.6 BLK barrel in production. It stabilizes everything from 150 to 180 gr supersonics to 210 through 300-plus gr subsonics. The trade is bullet construction: thin-jacketed varmint-style bullets can come apart in a 1:3 bore at supersonic speed, so run bullets made for 8.6 BLK or solid copper. If you want the slower SAAMI-standard twist for broader supersonic bullet choice, Faxon also makes 1:6 8.6 BLK barrels.

What gas block and gas tube does it take?

A .875″ gas block on the 1.9″ journal and a pistol-length gas tube. Faxon makes a .875″ adjustable and a .875″ fixed low-profile block, and a 304 stainless pistol-length gas tube. The gas port is reamed to .078″.

What does 4150 CMV mean?

Chrome-moly-vanadium steel with about 0.50% carbon, the alloy the M4 and M16 barrel specification calls for. The higher carbon and the vanadium give it more strength and wear resistance at temperature than 4140, which matters most on a barrel that will see fast strings and sustained fire.

Is the nitride inside the bore?

Yes. Salt-bath QPQ nitride is a diffusion treatment, not a plating, so it hardens the surface of the bore and the exterior while adding virtually nothing to it: the surface grows by a few ten-thousandths of an inch, .0002–.0004″, roughly a tenth the width of a human hair or about the diameter of a single red blood cell. It also gives the barrel its corrosion resistance and matte black finish.

Does it come with a gas block, gas tube, or muzzle device?

No. It ships with the black-oxide DPMS-pattern .308 extension installed, torqued, pinned, and headspaced. Gas block, gas tube, and muzzle device are sold separately; the muzzle is threaded M18x1.5.

Will it work with a suppressor?

Yes. The M18x1.5 muzzle takes a .36-cal-rated can on an M18x1.5 HUB adapter or taper mount, never a .30-cal can, and the cartridge was built for it: subsonic 8.6 BLK through a can is the quiet end of centerfire, and pistol-length gas with an adjustable block is what lets one upper run subs suppressed and supers bare. For a gun that runs suppressed most of the time, pair it with the Faxon .875″ adjustable gas block so you can bring the gas down.

What muzzle devices fit an M18x1.5 barrel with a tapered shoulder? Can I use a 5/8x24 device?

Any M18x1.5 device with a .338″ or larger bore: Faxon’s MuzzLok 8.6 BLK 3-port brake and Plan B M18 brake, the titanium or stainless M18 HUB adapter for any HUB-pattern can, or an M18 taper mount such as the JMac 360 taper mount Faxon sells, which seats on the 20° shoulder instead of a flat face. A 5/8x24 device needs a thread adapter, and a .30-cal bore will not pass a .338 bullet, so a 5/8x24 adapter only makes sense for a .36-cal-or-larger device or can. The barrel ships with a taper adapter, which is not a thread adapter: it is an unthreaded ring that seats on the 20° tapered shoulder and gives a conventional flat-shouldered M18x1.5 device a square face to torque against. Taper-mount devices seat directly on the shoulder and do not use it. No thread protector is included.

How fast does 8.6 BLK leave a 12″ barrel?

Subsonic loads of 210 to 300-plus gr leave at roughly 950 to 1,040 fps, which is by design and does not change much with barrel length; that is 450 to 600 ft-lb delivered by a bullet spinning fast enough to fragment. Supersonic 150 to 180 gr loads run roughly 1,900 to 2,100 fps from a 12″, depending on the load, within about 100 fps of a 16″. The SAAMI reference load is a 200 gr bullet at 2,200 fps. Faxon’s 8.6 BLK guide lists what to expect from each length.

Can I put a 12″ barrel on my AR-10?

A barrel under 16″ makes the firearm either a pistol or a short-barreled rifle under federal law. Build it on a lower that has only ever been a pistol, or on a lower registered as an SBR with an approved Form 1 or Form 4, and check your state law before you buy. Faxon cannot advise on your specific configuration.

Is the gas journal dimpled for set screws?

No. The journal ships round so any .875″ low-profile, clamp-on, or pinned gas block fits the 1.9″ journal. A set-screw block holds on the nitrided journal when its screws are torqued with thread locker; if you want dimples, mark them through the block’s screw holes and drill.

Where is it made, and what is the warranty?

Made in Greater Cincinnati, Ohio, from bar stock to finished barrel, and covered by the Faxon Lifetime Guarantee.

Dimensions are from the Faxon engineering print and inspection sheets for this SKU; weight is nominal. Gas block, gas tube, and muzzle device sold separately. Owner reviews are quoted as written from FaxonFirearms.com product reviews; press quotes link to their sources. Award: Shooting Sports Retailer Choice Awards, Favorite Aftermarket Barrel, Gold. Covered by the Faxon Lifetime Guarantee.