FAXON DUTY SERIES GUNNER PROFILE 11.5" MID-LENGTH 5.56 NATO AR15 BARREL

Rifle Barrels › Duty Series › 5.56 NATO / .223 › 11.5″ Gunner, Mid-Length  |  Works with: 5.56 BCG • .625″ gas block • mid-length gas tube • 1/2x28 muzzle devices • 5.56 suppressors

Why Mid-Length Gas on an 11.5″ Barrel

An AR’s gas system is a timing device. Where the port sits decides how much pressure reaches the carrier and for how long, and that decides how hard the bolt unlocks, how fast the carrier moves, and how much gas comes back through the receiver. A carbine-length port on an 11.5″ barrel opens about 7.7″ from the breech with four inches of barrel past it, so it sees high pressure for a long time; that is why a carbine-gas SBR runs anything you feed it and why it is harsh, especially suppressed. This barrel moves the port to 9.66″. Pressure there is lower and the bullet exits sooner after the port opens, so the carrier gets a gentler, shorter push. The bolt unlocks later, when chamber pressure has fallen further, extraction is easier on the brass, the reciprocating mass moves slower, and with a suppressor on there is noticeably less gas venting at the charging handle and ejection port. Faxon reams the port to .110″, larger than the .081″ on a 16″ mid-length, so that roughly two inches of dwell still deliver enough gas to run the gun.

The trade is margin. A carbine-gas 11.5″ is overgassed on purpose; this one is built to be tuned, and it rewards it. Around the shop it has a nickname, the gamer barrel, because the shooters who set it up with an adjustable gas block, pick a buffer, and dial it to their ammunition and their can end up with one of the softest 5.56 SBRs there is. That is exactly the gun a SWAT team wants: an 11.5″ that runs suppressed all day without beating up the shooter or the bolt. If you would rather have the margin than the tuning, the same profile is available with carbine-length gas, and the 10.5″ SOCOM is the heavier-contour option for a carbine-gas SBR.

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 .2195″ 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 six grooves, right-hand, one turn in 8 inches, to a .2250″ 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 .625″ gas journal is turned to .6240–.6247″ and checked with a micrometer on every barrel, held within .005″ of the bore, the straight .625″ section is turned true to the same axis, and the 1/2x28 muzzle is threaded and crowned. Then the breech end: the Government taper, the .980″ chamber journal, and the extension thread.
5. Chamber The 5.56 NATO 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 .110″ gas port is drilled and reamed through the .625″ journal, the M4 extension is torqued to 150 ft-lb and pinned, and the barrel is headspaced with a 5.56 go/no-go gauge.
8. Mark The Faxon shield and order number are laser-engraved on the chamber journal and “5.56 NATO 1-8T” 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 19 reviews on FaxonFirearms.com. Elsewhere: the 5.56 Gunner family averages 4.6 stars across 68 reviews at OpticsPlanet, and the Duty Series 5.56 line holds 4.7 stars across 25 reviews at MidwayUSA.

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 11.5″ Gunner 5.56 FAQs

Is this a 5.56 NATO or .223 Remington chamber?

5.56 NATO, headspaced with a 5.56 go/no-go gauge after the extension is installed. A 5.56 chamber has the longer throat that lets it fire both 5.56 NATO and .223 Remington safely; the reverse is not true, so a .223-chambered barrel should not be fed 5.56.

Why mid-length gas on an 11.5″ barrel, and what does it change?

Almost every 11.5″ 5.56 uses carbine gas, with the port about 7.7″ from the breech and four inches of barrel past it. This barrel puts the port at 9.66″, two inches farther out, where pressure is lower and the bullet leaves the muzzle sooner after the port opens. Less pressure for less time means a gentler push on the carrier, a later unlock, less bolt velocity, and, with a suppressor on, much less back pressure and gas at the charging handle. To make that work with only about two inches of dwell, Faxon reams the port to .110″ instead of the .081″ on a 16″ mid-length. The trade is margin: a carbine-gas 11.5″ is overgassed on purpose so it runs anything, while this one is built to be tuned. Pair it with an adjustable gas block, set it for your ammunition and your can, and it is one of the softest-shooting 5.56 SBRs you can build.

What is the Gunner profile on this barrel?

Faxon’s hybrid contour: a full .980″ chamber journal, a Government taper behind the gas block where the steel stiffens the barrel, then a .625″ gas journal and a straight .625″ section to the muzzle shoulder. On an 11.5″ it weighs 1.14 lb, keeps the weight between your hands instead of at the muzzle, and leaves a full shoulder for a muzzle device or suppressor mount.

What bullet weights does the 1:8 twist stabilize?

Everything from 55 gr FMJ through 69 and 77 gr match bullets. 1:8 is the most versatile twist for a general-purpose 5.56; 1:7 is only needed for the longest tracer and 80-plus grain projectiles, and 1:9 starts to run out of spin above 69 gr.

What gas block and gas tube does it take?

A .625″ gas block on the 1.5″ journal and a mid-length gas tube. Faxon makes a .625″ adjustable and a .625″ fixed low-profile block, and a 304 stainless mid-length gas tube. The gas port is reamed to .110″.

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 M4 extension installed, torqued, pinned, and headspaced. Gas block, gas tube, and muzzle device are sold separately; the muzzle is threaded 1/2x28.

Will it work with a suppressor?

Yes. The 1/2x28 muzzle takes any 5.56 direct-thread can or mount, and mid-length gas is why this barrel shoots so softly with a can: less back pressure, later unlock, less gas at your face than any carbine-gas 11.5″. For a gun that runs suppressed most of the time, pair it with the Faxon .625″ adjustable gas block so you can bring the gas down.

Do I need an adjustable gas block?

Yes, if you want this barrel to do what it is built for. The .110″ port is sized so the barrel runs unsuppressed with full-power ammunition; add a suppressor, change buffers, or switch to lighter loads and the right amount of gas changes. An adjustable block lets you set it once for each configuration, and most owners report a few minutes of tuning on the range. Faxon’s .625″ adjustable gas block is 1″ long, so it fits the 1.5″ journal with room; check the length of any other adjustable block before you buy, because a block longer than about 1.4″ will hang off the journal on this barrel.

Will it run unsuppressed?

Yes. The enlarged .110″ port is there so the barrel cycles unsuppressed with 5.56 NATO and full-power .223 loads and a standard carbine buffer. Where it wants an adjustable block is at the edges: very light or slow ammunition unsuppressed, or a suppressor with a heavy buffer. Tune it for the setup you shoot most and it is reliable in that setup.

How fast does 5.56 leave an 11.5″ barrel?

Roughly 2,700 to 2,800 fps with 55 gr ammunition and 2,600 to 2,700 with 62 gr, depending on the load, or about 300 fps less than a 16″. The extra inch over a 10.5″ buys about 50 to 75 fps and, on this barrel, the room for a mid-length gas system.

Can I put an 11.5″ barrel on my AR?

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.

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.