FAXON DUTY SERIES GUNNER PROFILE 20" RIFLE-LENGTH .308 WIN AR10 BARREL

Rifle Barrels › Duty Series › .308 Win › 20″ Gunner, Rifle-Length  |  Works with: .308-family BCG • .750″ gas block • rifle-length gas tube • 5/8x24 muzzle devices • .30 cal suppressors

Why a 20″ Rifle-Gas .308 Gunner

Twenty inches is where a .308 AR gives up nothing. It is the length the cartridge was developed at, so published ballistics are its ballistics: a 168 gr match bullet at about 2,650 fps that stays supersonic well past 1,000 yards, a 175 gr at about 2,600, and a 150 gr hunting bullet at 2,750 that expands past 500. It carries a full rifle-length gas system with seven inches of barrel past the port, the gentlest impulse and cleanest brass a .308 AR can produce, and it gives a scope the longest sight radius and the most stable platform in the line. The price of a 20″ has always been weight at the muzzle, which is why most 20″ AR-10s are range and prone rifles that nobody wants to carry.

The Gunner profile, which Faxon called the Big Gunner on AR-10 barrels until it simplified its naming in 2026, is how a 20″ loses that weight. 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 it; a .750″ gas journal and a .600″ section ahead of it strip the mass that a straight heavy profile carries at the muzzle for no return. At 2.24 lb it is lighter than most heavy-profile 16″ AR-10 barrels and a pound or more lighter than the 20″ barrels it replaces, so the rifle balances at the magazine well instead of the handguard. One owner who built it as an SPR calls the profile the balance point between sturdy enough for a suppressor and extended strings and light enough to shoot unsupported; another shot a 1.125″ group at 100 yards with the first four under an inch; a third hunts with it at under MOA with handloads. If the rifle needs to be shorter, the 18″ rifle-gas Gunner keeps the gas system and gives up about 50 fps; the 16″ mid-length Gunner is the carbine.

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, so the rifled dimensions Faxon air-gauges before treatment are the dimensions you get. 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. Extension, gas port, pin The DPMS-pattern .308 extension is torqued to 150 ft-lb, the .093″ gas port is drilled and reamed through the .750″ journal, the extension is pinned, and the barrel is headspaced with a .308 go/no-go gauge.
7. Nitride and mark Salt-bath QPQ nitride inside and out, then 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 8 reviews on FaxonFirearms.com. Elsewhere: Faxon’s .308 Gunner barrels average 4 stars across 13 reviews at OpticsPlanet.

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 20″ 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; one owner feeds this barrel a hoard of mixed surplus M80 and reports it shoots that better than the heavier barrel it replaced. Headspace is set at the factory; owners who check it with their own gauges and a Faxon, Toolcraft, or Aero bolt report it passes.

Why rifle-length gas on a 20″ .308?

Because it is the gas system the .308 AR was designed with, and 20″ is the length it was designed at. The cartridge pushes twice the gas of a 5.56 at the port, and a short gas system on a big-bore AR is what produces the violent, bolt-battering cycle AR-10s are known for. Rifle-length gas puts the port about 13.2″ from the breech with seven inches of barrel past it, the longest dwell of any Faxon .308 barrel, where pressure is lowest of any AR system, so the carrier gets a long, gentle push: the bolt unlocks later, brass comes out with the rim intact, the reciprocating mass moves slower, and the rifle stays on target through the recoil. Faxon reams the port to .093″. Owners run it with a standard AR-10 carbine buffer; one reports brass at two to three o’clock with a 5.6 oz buffer, so if yours ejects forward, step up a buffer weight or fit the adjustable block. This barrel needs a rifle-length gas tube; on a DPMS-pattern upper the standard rifle-length tube reaches the port.

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, then a .600″ section tapering to .575″ toward the muzzle where mass adds weight without adding stiffness. On a 20″ .308 it weighs 2.24 lb, against three and a half to four pounds for the heavy-profile 20″ barrels most AR-10s are built with, and it takes the most common AR gas block.

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 20″ barrel a 168 gr match bullet leaves at about 2,650 fps, which keeps it supersonic well past 1,000 yards.

What gas block and gas tube does it take?

A .750″ gas block on the 1.9″ journal and a rifle-length gas tube. Faxon makes a .750″ adjustable and a .750″ fixed low-profile block, and a 304 stainless rifle-length gas tube. The gas port is reamed to .093″.

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 without adding thickness or changing the rifled dimensions that were air-gauged before treatment. 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 rifle-length gas is the friendliest AR-10 system for suppressed use, with the least back pressure and the least gas at the charging handle. For a rifle that runs suppressed most of the time, pair it with the Faxon .750″ adjustable gas block so you can bring the gas down.

How fast does .308 leave a 20″ barrel, and is it worth the length?

Roughly 2,750 fps with 147 and 150 gr, 2,650 with 168 gr, and 2,600 with 175 gr, depending on the load: about 50 fps more than an 18″ and 125 more than a 16″. Those are the published numbers for the cartridge, because 20″ is the length .308 data is generated at, and they keep a 175 gr match bullet supersonic past 1,100 yards and a 150 gr hunting bullet expanding past 500. Whether it is worth two inches over the 18″ depends on the rifle: for a prone or bench rifle, a DMR, or a long-range hunting gun, the velocity and the sight radius are worth it; for a rifle that gets carried in timber or shot from a blind, the 18″ gives up little.

Which gas tube and buffer does it take?

A rifle-length gas tube, which on a DPMS-pattern upper is the standard rifle tube; Faxon’s 304 stainless rifle-length tube fits. Owners run a standard AR-10 carbine buffer and spring in a carbine receiver extension or a rifle buffer in an A2 stock. The port is reamed to .093″; if brass ejects forward of three o’clock, the rifle is a little over-gassed for that load, and a heavier buffer or the adjustable gas block brings it back.

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.