FAXON DUTY SERIES PENCIL PROFILE 16" MID-LENGTH 5.56 NATO AR15 BARREL

Rifle Barrels › Duty Series › 5.56 NATO / .223 › 16″ Pencil, Mid-Length  |  Works with: 5.56 BCG • .625″ gas block • mid-length gas tube • 1/2x28 muzzle devices • 5.56 suppressors

Why the Pencil Profile

Every ounce at the muzzle end of an AR is an ounce you swing, hold up, and carry, and the barrel is where most of it lives. The Pencil profile is the original lightweight AR barrel contour, and Faxon’s version removes everything the barrel does not need to shoot straight: a .980″ chamber journal for the extension and barrel nut, a body that tapers behind the gas block, a .625″ journal 1.1″ long for a low-profile block, and a taper from .625″ down to .525″ on the way to a .615″ muzzle shoulder for the thread. What is left weighs 1.20 lb, about three ounces less than the Gunner and half a pound less than the SOCOM, and it is enough steel to shoot MOA with ammunition the barrel likes.

Every barrel opens its group as it heats; a thin one simply gets there sooner, because it has less mass to soak up the heat. The same low thermal mass is why a Pencil cools faster than a Gunner or SOCOM once you let it sit. What a Faxon Pencil does not do is walk. Point of impact stays put and it does not throw stringers as it warms, because the rifled blank is stress relieved before it is ever turned to this profile, so the thin sections have no locked-in stress to release, and the OD is machined true to the bore so the barrel expands evenly instead of bending. Owners and reviewers keep reporting the same thing: it cools quickly and it shoots to the same place warm as it does cold. Every barrel is also 100% wet magnetic particle inspected, which finds the surface and near-surface flaws a thin wall cannot afford. It is not a benchrest profile. It is a barrel that lets you build a five-pound rifle and still hit what you aim at, and for a lightweight carbine, a hunting or truck rifle, or a smaller-framed shooter, that is the right trade. If the rifle’s job is mag dumps and training days, the 16″ Gunner keeps most of the weight savings with more steel where the heat is.

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 Pencil 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 forward taper is turned from .625″ to .525″, and the 1/2x28 muzzle is threaded and crowned. Then the breech end: the rear 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 .081″ 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 35 reviews on FaxonFirearms.com. Elsewhere: 4.9 stars across 47 reviews at OpticsPlanet, 4.9 across 9 at Brownells, 5.0 across 4 at Primary Arms, and 4.7 across 25 for the Duty Series 5.56 line 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″ Pencil 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 a 16″ barrel?

Because it puts the port about two inches farther from the chamber than carbine-length gas, so the system taps the bore at lower pressure. On a 16″ barrel that means a softer, more linear recoil impulse, less wear on the bolt and buffer, and better manners with a suppressor. Mid-length is the right gas system for a 16″ 5.56, and this barrel needs a mid-length gas tube.

What is the Pencil profile, and is it rugged enough?

The lightest AR-15 barrel contour: a .625″ gas journal with the body tapered on both sides of it, down to .525″ ahead of the block. At 1.20 lb it is Faxon’s lightest 16″ 5.56 barrel. It is more rugged than its profile suggests because the blank is stress relieved before it is turned thin and every barrel is 100% wet MPI inspected, so there is no locked-in stress to shift under heat and no hidden flaw in the wall. Like any barrel its group opens as it heats, and with less thermal mass it gets warm sooner and cools sooner; what it does not do is shift point of impact or string shots, because the blank is stress relieved before the profile is turned. It is not a benchrest profile, but it shoots MOA with ammunition it likes and is the right barrel for a lightweight build, a hunting or truck rifle, or a smaller shooter’s carbine.

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 1.1″ 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 .081″.

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, and keep it light. The 1/2x28 muzzle takes any 5.56 can or mount, but a heavy suppressor on a Pencil barrel puts the weight right back where the profile took it off. Faxon recommends the Harmonix Ion 5.56, a titanium can, for Pencil builds. Mid-length gas is the friendlier system for suppressed use; for a rifle that runs suppressed most of the time, pair it with the Faxon .625″ adjustable gas block so you can bring the gas down.

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.