Pinned Gas Block Barrels

Why Pin a Gas Block?

Most low-profile gas blocks are held on with set screws. Heat cycles and recoil can loosen those screws over time, and if the block rotates or slides even slightly, the gas port and the block no longer line up. The rifle short-strokes or stops cycling, usually at the worst time. Pinning the block through a notch in the gas journal locks it mechanically, so it cannot walk.

Pinning a block yourself normally means a drill press, a fixture, and a good chance of drilling into the journal off-center. Faxon does the precise part for you: the journal is notched at the factory and the matching block is pre-drilled to line up with it. You get the reliability of a pinned block with nothing to drill.

What’s in the Box and How to Install It

Each barrel ships with its M4 barrel extension installed, torqued, pinned, and headspaced, plus a Faxon fixed low-profile gas block and its retaining pin, packed separately and uninstalled. The gas tube and muzzle device are sold separately.

1. Barrel and barrel nut: Install the barrel in the upper and torque the barrel nut to your handguard maker’s spec.
2. Gas tube and block: Fit the gas tube to the block, feed the tube through the barrel nut into the upper, slide the block onto the journal, and align it with the gas port.
3. Pin it: Line up the pre-drilled hole with the notch in the journal, snug the set screws, and drive the pin.
4. Handguard: Slide on a free-float handguard that clears a low-profile gas block and lock it to the barrel nut. The block has to be pinned first: once the handguard is on, it covers the block and you can’t reach the pin.

You can drive the pin back out later, but a pinned block is designed to be installed once and left alone.

Compare the Pinned Gas Block Barrels

Every Pinned Gas Block barrel is built on the matching Duty Series barrel; the last column links the standard version without the block and pin.

Choosing a Profile and Gas Length

Gunner. Faxon’s Gunner profile puts steel where a barrel needs stiffness, at the chamber and under the handguard, and trims it out front. You get Government-profile durability with close to Pencil-profile handling, which is why it is Faxon’s most popular contour.

Pencil. 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.

SOCOM. The SOCOM profile is a heavier contour with extra steel ahead of the gas block. It soaks up heat on long strings and keeps a short or hard-used carbine steady, at the cost of some weight.

Gas length. The 16″ and 14.5″ barrels run mid-length gas, which moves the port farther from the chamber for a softer, smoother impulse and less wear on the bolt. The 10.5″ 5.56 barrels run carbine gas, the standard for that length. The 10.5″ 300 Blackout runs pistol-length gas, which gives a short 300 BLK barrel enough dwell time to cycle with or without a suppressor. Grab the matching mid, carbine, or pistol gas tube.

Fixed or adjustable? These barrels come with a fixed block, the simple, reliable choice for an unsuppressed rifle with a standard carrier. If you plan to run a suppressor or a lightweight carrier, Faxon recommends its patented adjustable gas block on a standard Duty Series barrel instead, so you can tune gas for your can and ammunition.

How Every Pinned Gas Block Barrel Is Made

1. Drill and ream: 4150 CMV bar 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: Profile turned, gas journal cut, then notched for the gas block pin
6. Thread and crown: Muzzle threaded (1/2x28 for 5.56, 5/8x24 for 300 BLK) with a target crown
7. MPI and nitride: 100% wet magnetic particle inspected, then salt-bath QPQ nitrided inside and out
8. Port and extension: Gas port drilled; M4 extension torqued, pinned, and headspaced
9. Gas block: Matching low-profile block pre-drilled for the pin and packed with the barrel

What Owners Say

Pinned Gas Block barrels average 4.9 out of 5 stars across 27 reviews on FaxonFirearms.com. Owners keep coming back to the same two things: the quality for the price, and not having to pin the block themselves.

Faxon AR-15 and AR-10 barrels have been voted Favorite Aftermarket Barrel by Shooting Sports Retailer every year since 2022, the Gold Award.

Pinned Gas Block Barrel FAQs

Is the gas block already pinned?

No. The block and pin ship in the box, uninstalled. The journal is already notched and the block is pre-drilled, so you slide the block on, align it with the port, and drive the pin. No drilling or fixture is needed.

Which gas block comes with each barrel?

A Faxon fixed low-profile gas block sized to the journal: .625″ on the Gunner and Pencil barrels, .750″ on the SOCOM barrels and the 300 Blackout.

Why pin a gas block instead of using set screws?

Set screws can loosen under heat and recoil. If the block shifts, the port and block no longer line up and the rifle can stop cycling. A pin through a notched journal locks the block in place.

Do I pin the gas block before or after the handguard?

Before. Torque the barrel nut, install the gas tube and block, and drive the pin, then slide on a free-float handguard that clears a low-profile block. The handguard covers the block, so you can’t reach the pin once it’s on. Since a pinned block is meant to stay put, settle on your barrel nut before you drive the pin.

Can I use an adjustable gas block instead?

Not on these barrels; they are set up for the included fixed block. For suppressed builds or lightweight carriers, choose a standard Duty Series barrel and Faxon’s patented adjustable gas block.

Does it come with a gas tube or muzzle device?

No. The gas tube and muzzle device are sold separately. The 5.56 barrels are threaded 1/2x28 and the 300 Blackout is threaded 5/8x24, all with a target crown.

Are the 14.5-inch and 10.5-inch barrels legal?

A barrel under 16″ makes the firearm a short-barreled rifle or an AR pistol depending on how it is configured, unless a muzzle device is permanently attached to bring a rifle barrel to at least 16″. Know and follow federal, state, and local laws before you build.

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: it hardens the bore and exterior and adds corrosion resistance while adding virtually nothing to the dimensions, and it needs little to no break-in.

Are these barrels full-auto capable?

Yes. Like every Faxon nitrided rifle barrel, they are full-auto capable. 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 and light barrels heat up faster, so expect to reach those limits sooner. If a barrel smokes or starts to glow, stop. Groups open up as any barrel heats; Faxon’s stress relieving keeps point of impact from walking, but let it cool before you check zero. Each product page has the full heat guidance.

Where are they made?

In Greater Cincinnati, Ohio, and every barrel is 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. MuzzLok® and HARMONIX® are trademarks of Faxon Firearms. Know and follow all federal, state, and local laws.