FAXON DUTY SERIES GUNNER PROFILE 13.9" MID-LENGTH .308 WIN AR10 BARREL

Rifle Barrels › Duty Series › .308 Win › 13.9″ Gunner, Mid-Length  |  Works with: .308-family BCG • .750″ gas block • mid-length gas tube • 5/8x24 muzzle devices • .30 cal suppressors

Why 13.9″ With Mid-Length Gas

Thirteen point nine inches is the shortest a .308 can be and still carry a mid-length gas system with real dwell behind it, and that is the whole argument for this barrel. A .308 is a big cartridge for the AR gas system: it pushes twice the gas of a 5.56, and every inch closer the port sits to the chamber the harder it hits the carrier. A 12.5″ or 10.5″ .308 has to run carbine or pistol gas and lives with the consequences, an adjustable block, a heavy buffer, and brass in the next lane. This barrel puts the port where the 16″ puts it, 9.8″ from the breech, and leaves four inches of barrel past it, which is enough dwell for a .086″ port to cycle factory ammunition on a standard AR-10 buffer without tuning. Velocity gives up about 100 fps to the 16″ with 168 gr, roughly 2,450 fps, which keeps a match bullet supersonic well past 800 yards; with a 6″ to 7″ .30-cal can on the muzzle the upper is about the length of a bare 18″ rifle. That is why the 13.9″ has become the short .308 for people who shoot theirs suppressed. Owners who want a rifle instead of a pistol or SBR pin and weld a full-length muzzle device to reach 16″; the FAQ below covers the math.

The Gunner profile, which Faxon called the Big Gunner on AR-10 barrels until it simplified its naming in 2026, is how a short .308 loses the weight without losing the stiffness. A 1.200″ extension shoulder, a .750″ body behind the gas block, and a .875″ step at the block keep the barrel stiff and give it heat capacity where a .30-caliber bore needs the wall; a .750″ journal and a taper from .600″ to .575″ ahead of it strip the weight a heavier profile carries at the muzzle for no return. At 1.80 lb it is two ounces under the 16″ Gunner and balances at the magazine well with a can on. Owners of this barrel report the same things they report on the 16″: fit and finish that drops in, and rails from 13″ to 13.5″ that land exactly at the muzzle with room for a suppressor mount. If you want the same gas system with no paperwork, the 16″ .308 Gunner is the carbine; the 16″ .308 Pencil is the lightest 16″; the 18″ Gunner is the rifle-gas choice.

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 .3015″ 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 four grooves, right-hand, one turn in 10 inches, to a .3095″ 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 .750″ gas journal is turned to .7490–.7497″ and checked with a micrometer on every barrel, held within .005″ of the bore, the forward section is turned from .600″ to .575″ true to the same axis, and the 5/8x24 muzzle is threaded and crowned. Then the breech end: the .750″ body, the .875″ step, the 1.200″ extension shoulder, and the 1-16 extension thread.
5. Chamber The .308 Win 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 .086″ gas port is drilled and reamed through the .750″ journal, the DPMS-pattern .308 extension is torqued to 150 ft-lb and pinned, and the barrel is headspaced with a .308 go/no-go gauge.
8. Mark The Faxon shield and order number are laser-engraved on the chamber journal and “.308 WIN 1-10T” 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 4 reviews on FaxonFirearms.com, and 4.2 across 5 for this exact barrel at OpticsPlanet; Faxon’s .308 Gunner line is also reviewed 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 13.9″ Gunner .308 FAQs

Is this a .308 Winchester or 7.62x51 NATO chamber?

.308 Winchester, headspaced with a .308 go/no-go gauge after the extension is installed. 7.62x51 NATO is loaded to lower pressure than commercial .308 and runs fine in it; it runs surplus M80 fine, though one owner notes his barrel groups match ammunition far better than M80, which is true of most .308s. Headspace is set at the factory with a go/no-go gauge after the extension is installed.

Why mid-length gas on a 13.9″ .308, and what does it need to run?

Because a .308 pushes twice the gas of a 5.56 at the port, and the closer the port sits to the chamber the harder it hits: a carbine or pistol port on a short .308 makes a violent cycle, battered brass, and a gun that does not want to stay on target. This barrel keeps the mid-length port in the same place as Faxon’s 16″ .308, about 9.8″ from the breech, so the system taps the bore at the same lower pressure; 13.9″ leaves about four inches of dwell past it, which is enough that Faxon reams the port to .086″, a few thousandths over the 16″’s .081″, and the barrel cycles factory .308 and 7.62 NATO on a standard AR-10 carbine buffer. It is the shortest .308 Faxon makes that keeps mid-length gas, and that is the reason to buy it over a shorter pistol-gas .308. If a suppressor is in the plan, an adjustable block lets you bring the gas back down. This barrel needs an AR-10 mid-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 .750″ body behind the gas block, a .875″ step and a .750″ gas journal at the block, and a taper from .600″ to .575″ ahead of it, on a blank that starts at a 1.200″ extension shoulder. At 13.9″ it weighs 1.80 lb, which is what a heavy-profile 16″ 5.56 barrel weighs, and it takes the same .750″ low-profile block as the rest of the line.

What bullet weights does the 1:10 twist stabilize?

The whole .308 range: 147 and 150 gr ball and hunting loads, 168 and 175 gr match bullets, and 180 gr hunting bullets. 1:10 is the .308 standard for a reason; 1:12 runs out of spin at the heavy end and 1:8 gains nothing with anything a gas gun feeds. From a 16″ barrel a 168 gr match bullet leaves at about 2,550 fps, which keeps it supersonic to about 1,000 yards.

What gas block and gas tube does it take?

A .750″ gas block on the 1.9″ journal and a mid-length gas tube. Faxon makes a .750″ adjustable and a .750″ fixed low-profile block, and a 304 stainless mid-length gas tube. The gas port is reamed to .086″.

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 5/8x24.

Will it work with a suppressor?

Yes. The 5/8x24 muzzle takes any .30-cal direct-thread can or 5/8x24 mount rated for .308, and mid-length gas is the friendlier system for a suppressed short .308, with less back pressure and less gas at the charging handle than carbine or pistol gas. For a gun that runs suppressed most of the time, pair it with the Faxon .750″ adjustable gas block so you can bring the gas down.

Can I put a 13.9″ 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.

Can I pin and weld a muzzle device to make it a 16″ rifle?

Yes, and some owners do. A rifle needs a barrel of at least 16″ measured from the closed bolt face to the end of a permanently attached muzzle device, so a 13.9″ barrel needs a device that adds at least 2.1″ beyond the muzzle, pinned and welded or high-temp silver soldered in place; a standard A2 adds about 1.75″ and will not get there, so it takes a full-length, fixed-body flash hider or suppressor mount. Measure with the device seated before it is welded and give yourself margin over 16″. Once it is done the device is part of the barrel and cannot be swapped, and a direct-thread suppressor is off the table unless the pinned device is a mount. Faxon’s MuzzLok devices use a locking extension nut and are not designed to be pinned and welded.

How fast does .308 leave a 13.9″ barrel, and what does it give up?

Roughly 2,500 to 2,600 fps with 147 and 150 gr, 2,400 to 2,500 with 168 gr, and 2,350 to 2,400 with 175 gr, depending on the load, or about 100 fps less than a 16″ and 225 less than a 20″. That keeps a 175 gr match bullet supersonic past 800 yards and a 150 gr hunting bullet expanding well past 300, which is more than a 14-inch gun will be asked to do.

Why 13.9″ instead of a 12.5″ or 16″ .308?

Gas. A 12.5″ .308 has to run a carbine port with two inches of barrel past it, which means a big port, a heavy buffer, an adjustable block, and a hard cycle; the 13.9″ keeps the 16″’s mid-length port with four inches of dwell and runs a standard buffer without tuning, at a cost of one and a half inches. Against the 16″ it gives up about 100 fps and the option of a rifle with no paperwork, and buys two inches with a can on and two ounces off the muzzle. Pick the 16″ for a rifle, the 13.9″ for a suppressed SBR or pistol, or for a rifle built around a permanently attached device.

Is the gas journal dimpled for set screws?

No. The journal ships round so any .750″ 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.