FAXON PINNED GAS BLOCK PENCIL PROFILE 10.5" CARBINE-LENGTH 5.56 NATO AR15 BARREL

Rifle Barrels › Pinned Gas Block Barrels › 10.5″ Pencil 5.56 NATO  |  Works with: carbine gas tube • 5.56/300 BLK BCG • 9″ handguard • 1/2x28 muzzle devices

What the Pinned Gas Block Adds

A low-profile gas block clamps to the journal with set screws. On most builds that works, but heat cycles and recoil can loosen the screws over time, and if the block shifts, the gas port no longer lines up and the rifle stops cycling. Pinning the block mechanically locks it to the barrel. Doing it yourself means drilling the block and the journal in perfect alignment, which takes a drill press, a fixture, and a careful setup.

Faxon does that part for you. The .625″ journal is notched for the pin, and the Faxon fixed low-profile gas block in the box is pre-drilled to match. Slide the block on, line it up with the port, snug the set screws, and drive the included pin. The block is then held by the screws and the pin, and it will not walk. Compared with buying the standard 10.5″ Pencil barrel ($175) and a .625″ fixed gas block separately, you add the pin and the machining for a small difference, and the hard part is already done.

One thing to plan for: a pinned block is meant to stay where it is. Install the barrel nut and handguard you want to run before you drive the pin, and choose a free-float handguard that clears a low-profile block.

The 10.5″ Pencil Profile and Carbine-Length Gas

The Pencil profile is Faxon’s lightest contour. It heats up quickly but also cools quickly, and because every Duty Series barrel is stress relieved and 100% wet magnetic particle inspected, it is a surprisingly rugged barrel that punches above its weight. It is not a benchrest profile, and it is not meant to be. Carbine-length gas is the standard system for a 10.5″ 5.56 barrel and cycles reliably across a wide range of loads.

The 5.56 NATO chamber runs both 5.56 NATO and .223 Remington ammunition, and the 1:8 twist stabilizes the common 55 to 77 gr bullets.

Built on the Duty Series

Pinned Gas Block barrels are built on Faxon’s Duty Series architecture: 4150 CMV steel, button rifled, stress relieved, 100% wet magnetic particle inspected, and salt-bath QPQ nitrided inside and out. Nitride is a diffusion treatment, not a plating. It hardens the bore and exterior while adding virtually nothing to them, a few ten-thousandths of an inch, roughly a tenth the width of a human hair, and it needs little to no break-in. Faxon AR-15 and AR-10 barrels have been voted Favorite Aftermarket Barrel by Shooting Sports Retailer every year since 2022, the Gold Award.

How it compares to Faxon’s other lines: Match Series is 416-R stainless with 5R rifling and the same nitride finish; MATCH-X takes 416-R further with a honed and lapped bore; and the Combat Series offers classic configurations with a manganese phosphate exterior and chrome-lined bore. Chrome lining still has its place, mainly sustained full-auto fire, but for most shooters nitride does what they need and more.

What’s in the Box

How It’s Made

1. Drill and ream: The 4150 CMV bar is gun-drilled and reamed.
2. Button rifle: Button rifled, 1:8 twist.
3. Air gauge: Bore air gauged.
4. Stress relieve: Stress relieved at the blank stage, then qualified true to the bore.
5. Profile and journal: Pencil profile turned and the .625″ journal cut, then notched for the gas block pin.
6. Thread and crown: 1/2x28 threads cut and a target crown.
7. Chamber: 5.56 NATO chamber cut.
8. MPI and nitride: 100% wet magnetic particle inspected, then salt-bath QPQ nitrided inside and out.
9. Port and extension: Gas port drilled; M4 extension torqued, pinned, and headspaced.
10. Gas block: The matching .625″ low-profile block is pre-drilled for the pin and packed with the barrel.

How We Inspect It

Faxon barrels are built to a written control plan, and each run is logged on inspection sheets. Here is what this barrel goes through before it ships.

What Owners Say

Average rating: 5.0 out of 5 stars from 3 reviews on FaxonFirearms.com. The standard 10.5″ Pencil barrel this one is built on has its own reviews too.

Build It Out: Faxon Parts That Fit This Barrel

Compare Your Options

See every barrel in this line on the Pinned Gas Block Barrels page.

Pinned Gas Block 10.5″ Pencil FAQs

Is the gas block already pinned?

No. The barrel ships with a Faxon .625″ fixed low-profile gas block and its retaining pin in the box, uninstalled. Faxon has already notched the journal and pre-drilled the block, so you slide the block on, align it with the gas port, snug the set screws, and drive the pin. No drilling or fixture is needed.

Why pin a gas block?

Set screws hold most low-profile gas blocks, and heat cycles and recoil can loosen them over time. If the block shifts, the port and block no longer line up and the rifle can stop cycling. A pin through the block and a notched journal mechanically locks the block in place.

What gas block comes with it?

A Faxon .625″ fixed (non-adjustable) low-profile gas block, the standard block for this barrel’s .625″ journal. If you want an adjustable block for suppressed use, choose the standard 10.5″ barrel with Faxon’s adjustable .625″ block instead.

Can I remove the gas block later?

Yes, by driving the pin back out, but a pinned block is meant to stay put. Install your barrel nut and handguard before you pin the block, and pick a free-float handguard that clears a low-profile block.

Does it come with a gas tube or muzzle device?

No. The gas tube (carbine-length) and muzzle device are sold separately. The muzzle is threaded 1/2x28 with a target crown.

Is a 10.5-inch barrel legal?

A barrel under 16″ makes the firearm an AR pistol or a short-barreled rifle, depending on how it is configured. Know and follow federal, state, and local laws before you build.

Is a Pencil profile durable?

Yes. It heats up quickly and cools quickly, and because the barrel is stress relieved and 100% wet magnetic particle inspected, it is surprisingly rugged and punches above its weight. It is not a benchrest profile and isn’t meant to be.

What does 4150 CMV and nitride mean?

4150 CMV is a chrome-moly-vanadium barrel steel known for toughness and wear resistance. Salt-bath QPQ nitride is a diffusion treatment, not a plating, so it hardens the bore and exterior while adding virtually nothing to them, and it needs little to no break-in.

Is it full-auto capable, and how much heat can it take?

Yes. Like every Faxon nitrided rifle barrel, it is full-auto capable. The barrel is stress relieved, magnetic particle inspected for flaws, and salt-bath nitrided at roughly 1,050°F, so the steel and the nitride are stable far beyond normal firing temperatures. What limits any barrel on automatic fire is heat. A good guideline, drawn from U.S. military guidance for the M4 carbine: about 12 to 15 rounds a minute can be fired indefinitely, and continuous rapid fire should stop at about 150 rounds so the barrel can cool. Short barrels heat up faster than a 16″ rifle barrel, so expect to reach those limits sooner. Push past that and throat wear speeds up, which shortens barrel life. If the barrel smokes or starts to glow, stop: near 1,000°F the steel is approaching the temperature it was nitrided at, where it can begin to soften and the nitride can lose hardness, and military testing has seen M4 barrels fail at about 1,360°F. A hot chamber can cook off a round in as little as 10 seconds, so clear it quickly or keep it pointed in a safe direction. And heat affects accuracy in every barrel: groups open up as it heats. Faxon’s stress relieving and machining keep point of impact from walking, but let it cool before you check zero or shoot for groups.

Where is it made, and what is the warranty?

Made in Greater Cincinnati, Ohio, and covered by the Faxon Lifetime Guarantee.

Full-auto heat guidance is general, based on published U.S. military rate-of-fire guidance and steel and nitride data, not Faxon testing; barrel life under automatic fire depends on rate of fire, ammunition, and cooling. Glock® is a registered trademark of Glock, Inc.; Faxon is not affiliated with Glock. HARMONIX® and MuzzLok® are trademarks of Faxon Firearms. Know and follow all federal, state, and local laws.