FAXON DUTY SERIES GUNNER PROFILE 16" CARBINE-LENGTH 300 BLK AR15 BARREL

Rifle Barrels › Duty Series › 300 BLK › 16″ Gunner, Carbine-Length  |  Works with: 300 BLK BCG • .750″ gas block • carbine-length gas tube • 5/8x24 muzzle devices • .30 cal suppressors

Why a 16″ 300 BLK, and Why the Gunner Profile

Most 300 BLK barrels are short, because the cartridge was built around a suppressed SBR. The 16″ is for the other job the cartridge does well: a hunting and general-purpose rifle that needs no tax stamp, in states that require a rifle and in hands that want one. Sixteen inches adds 150 to 250 fps over a pistol-length barrel with 110 to 125 gr supersonics, which is the margin that keeps an expanding bullet above its opening velocity out past 200 yards, and it adds a long sight radius and a full-length handguard. What it does not add is much noise or recoil: 300 BLK from a 16″ is still a soft-shooting .30 that runs on a standard 5.56 bolt and magazine.

A .30-caliber bore takes more steel out of a barrel than a .22-caliber one does, so Faxon’s 300 BLK Gunner is not a straight copy of the 5.56 Gunner: it keeps a .845″ body behind the gas block, runs a .750″ gas journal instead of .625″, and tapers to .625″ ahead of the block. The chamber journal and body are where a barrel gets its stiffness; the taper is where a barrel gets heavy without getting stiffer. At 16″ the result is 1.48 lb, about what a heavy-profile 14.5″ 5.56 weighs, in a rifle that balances at the magazine well. If the rifle will live with a suppressor and shoot mostly subsonics, the 10.5″ Gunner with pistol-length gas is the better tool; Faxon’s 300 Blackout barrel guide walks through length, twist, and setup for every use.

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 8 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 Gunner taper ahead of it is turned true to the same axis, and the 5/8x24 muzzle is threaded and crowned. Then the breech end: .845″ body, .980″ chamber journal, and the extension thread.
5. Chamber The 300 BLK chamber is cut and checked with a headspace gauge; chamber surfaces are held to a 20 Ra finish.
6. Extension, gas port, pin The M4 extension is torqued to 150 ft-lb, the .120″ gas port is drilled and reamed through the .750″ journal, the extension is pinned, and the barrel is headspaced with a 300 BLK 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 “.300 BLK 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 9 reviews on FaxonFirearms.com. Elsewhere: Faxon’s 300 BLK Gunner family averages 4.7 stars across 51 reviews at OpticsPlanet, and the line has a dozen owner reviews at Brownells and eleven 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 16″ Gunner 300 BLK FAQs

Is this a 300 BLK or 300 Whisper chamber, and what should I know about running it next to 5.56?

It is a SAAMI 300 AAC Blackout chamber, headspaced with a 300 BLK go/no-go gauge after the extension is installed. It will chamber and fire 300 Whisper ammunition, but load to 300 BLK data. The thing to know: a 300 BLK round will chamber in a 5.56 barrel and destroy the rifle when fired. If you own both, keep the magazines and the uppers visibly different and never mix them on the bench.

Why carbine-length gas on a 16″ 300 BLK, and will it cycle subsonics?

On a 16″ barrel, carbine-length gas puts the port about 7.4″ from the breech with nearly nine inches of barrel past it. 300 BLK is a low-pressure cartridge that is done burning powder by about nine inches, so the port has to sit early to catch enough gas, and Faxon reams it to .120″, larger than the .104″ on the pistol-length barrels, to make up for the lower pressure at a carbine port. With 110 to 125 gr supersonics it cycles unsuppressed with a standard carbine buffer. Subsonics are a different matter on any 16″ 300 BLK: with a suppressor adding back pressure they generally run; unsuppressed, a 1,000 fps load through a carbine-gas 16″ is marginal and depends on the load and buffer. If subsonics unsuppressed are the plan, a shorter pistol-gas barrel is the better tool; for a 16″ that shoots supersonics and suppressed subs, this is the right system, and this barrel needs a carbine-length gas tube.

What is the Gunner profile, and why is the 300 BLK version different from the 5.56?

Faxon’s hybrid contour: full diameter where the barrel gets its stiffness (the chamber journal and the body behind the gas block) and tapered ahead of the block where mass only adds weight. Because a .30-caliber bore leaves less wall than a .22, the 300 BLK Gunner keeps a .845″ body and a .750″ gas journal, where the 5.56 Gunner runs .750″ and .625″. That is why it weighs 1.48 lb at 16″ against 1.37 lb for the 5.56 Gunner, and why it takes the most common AR gas block.

What bullet weights does the 1:8 twist stabilize?

Both ends of the cartridge: 110 to 125 gr supersonic loads and 190 to 220 gr subsonics. 1:8 is the do-everything 300 BLK twist and the one most factory ammunition is loaded for. For a 16″ that will mostly shoot supersonics at deer, hogs, and steel, it is the right choice.

What gas block and gas tube does it take?

A .750″ gas block on the 1.9″ journal and a carbine-length gas tube. Faxon makes a .750″ adjustable and a .750″ fixed low-profile block, and a 304 stainless carbine-length gas tube. The gas port is reamed to .120″.

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 M4 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, and on a 16″ carbine-gas 300 BLK the can is also what makes subsonics cycle reliably, so it is the natural partner for this barrel. 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 300 BLK leave a 16″ barrel, and how far will it hunt?

About 2,300 to 2,400 fps with 110 gr supersonics and 2,200 to 2,300 with 125 gr, depending on the load, or 150 to 250 fps more than a pistol-length barrel. That margin matters for hunting: most 110 to 125 gr expanding bullets need roughly 1,700 to 1,800 fps to open, which a 16″ delivers out to about 200 yards. Subsonics leave at about 1,000 fps from any length and are a suppressed, short-range proposition. Faxon’s 300 Blackout barrel guide covers the trade-offs at every length.

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. 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.