FAXON PATENTED ADJUSTABLE .750" 3 SCREW LOW PROFILE GAS BLOCK

How the Faxon Adjustable Gas Block Works

An AR-15 is gas operated: propellant gas leaves the barrel through a small port under the gas block, travels down the gas tube, and drives the bolt carrier rearward. Every barrel is ported for a worst-case load with no suppressor. Add a can, run hotter ammunition, or fit a lighter carrier, and the rifle is overgassed — harder recoil, more gas in your face, faster wear. An adjustable gas block lets you meter that gas to what the rifle actually needs.

Conventional adjustable blocks meter gas with a screw that threads into the gas passage. That screw lives in the hottest, dirtiest spot on the rifle, and carbon packs into its threads until it will not turn. Faxon’s design takes the screw out of the gas path entirely. Gas exits the barrel port into the block’s passage as it would in any fixed block. The difference is that the gas tube is not fixed: it passes through the block and is pinned to a nitrided 4140 adjustment plate on the rear of the block. Turning the adjustment screw slides the plate, and the tube with it, forward or rearward. That shifts the tube’s inlet hole relative to the block’s gas passage, opening or closing the effective port. With the tube fully forward, the port is closed. Fourteen clicks rearward, with the tube at its deepest in the gas key, it is wide open.

Each click is a real detent: a spring inside the adjustment mechanism presses into notches machined into the screw head, so you feel every setting, the block holds it under recoil, and you can count back to a known setting without a reference mark. The adjustment screw takes a 3/32″ hex key or a flat screwdriver, and because it carries no carbon, the same tool works on it in year five.

What’s Included

What Reviewers and Owners Say

Here is what independent press and verified owners have said about the Faxon adjustable gas block, starting with owners of this .750″ size.

Average ratings, out of 5 stars: 4.9 on FaxonFirearms.com, 4.7 at OpticsPlanet, and 5.0 at AT3 Tactical.

Tuning the Gas Setting

Start fully open (tube all the way rearward) and confirm the rifle runs. Then close the block one click at a time, firing a few rounds at each setting, until the bolt fails to lock back on an empty magazine. Open it back up one or two clicks. That is your setting for that ammunition, buffer, and suppressor combination; note the click count so you can return to it. Retune when you add or remove a suppressor or change to a very different load.

Adjust with the rifle unloaded and the block cool. Because the screw never touches gas-port carbon, no cleaning or heat is needed before turning it.

Installation

Tools: small hammer, flat punch, roll-pin punch, and the free 3D-printed assembly fixture (a padded vise works). The gas tube and its roll pin are sold separately.

Faxon .750″ Adjustable Gas Block FAQs

What barrels does the .750″ gas block fit?

Any AR barrel with a .750″ gas journal, which is the most common size on AR-15 and AR-10 barrels and covers most standard and mid-weight profiles; each Faxon barrel page shows the gas block diameter it needs. Thinner-profile barrels, such as Faxon’s Pencil and Gunner profiles in 5.56 and .223 Wylde, use a .625″ journal (GBA-LP-625-3), and heavier profiles use .875″ (GBA-LP-875-3). Measure the journal with calipers if you are not sure.

How is this different from other adjustable gas blocks?

Other designs meter gas with a screw threaded into the gas passage, where carbon fouls the threads and eventually seizes the screw. Faxon’s patented design leaves the gas passage alone and moves the gas tube instead: the tube is pinned to an adjustment plate, and the screw slides the plate to open or close the port. The screw never contacts gas-port carbon, so it keeps turning freely.

Are the 14 settings real detents?

Yes. A spring inside the adjustment mechanism engages notches machined into the adjustment screw head. Each click is a positive stop you can feel and count, and the detent holds the setting under recoil without a locking screw or thread locker.

Does it come with a gas tube?

No. The block uses any standard AR gas tube in pistol, carbine, mid, or rifle length, so you can reuse the one you have. The gas tube roll pin comes with the gas tube. Faxon stainless gas tubes are sold separately.

Does it work suppressed?

That is the main reason to own one. A suppressor raises back-pressure and overgasses the rifle; closing the block a few clicks brings cycling speed, recoil, and gas blowback back to normal. Because the adjustment screw stays out of the carbon, it is still easy to open back up when you take the can off.

Will it fit under my handguard?

The block is 1.000″ long, .899″ wide, and 1.350″ tall from the bottom of the block to the top of the gas tube boss on a .750″ journal. That clears the large majority of free-float handguards. The adjustment screw is on the rear face of the block, so you adjust it from the receiver side through the handguard’s slots with a 3/32″ hex key.

Can I install it myself?

Yes, with a hammer, a flat punch, and a roll-pin punch. The one extra step compared with a fixed block is that the tube is pinned to the adjustment plate rather than the block body, so set the plate fully forward (fully closed) before you pin it. Faxon offers a free 3D-printable fixture that holds the block square while you drive the pin, and the installation video above walks through every step.

Does moving the gas tube cause a problem with the bolt carrier’s gas key?

No, and the reason is in the mil-spec drawings. The gas key and gas tube were never designed as a fixed joint: every time the rifle fires, the key slides several inches off the tube and back on, guided by a chamfered mouth, with clearance between the tube’s .180″ receiver end and the key’s .1805″ bore. The tube is only ever a slip fit in the key. The Faxon block moves the tube a total of .125″ (1/8″, about the thickness of two stacked pennies) from fully closed (tube forward) to fully open (tube rearward, deepest in the key). Mil-spec gas key and gas tube tolerances already allow for that much movement, and Faxon’s patent spells it out: the small shift in the tube’s rear position keeps it engaged in the gas key, with negligible effect, if any, on how the gas system runs. The tube stays fully engaged at every setting, and Faxon validated the block across the full adjustment range before release.

Is the Faxon adjustable gas block patented?

Yes. The design is protected by U.S. Patent No. 12,716,670 B2, “Adjustable Gas System,” issued August 25, 2026 and assigned to Faxon Firearms. The patent covers the core of how this block works: a gas tube that slides inside the block so its inlet moves into or out of line with the gas passage, a threaded adjustment screw held captive on the block so turning it moves the tube instead of entering the gas stream, and a detent that holds the screw at discrete settings.

Where is it made and what is the warranty?

Machined from 4140 chromoly steel and flash nitrided in the USA by Faxon Firearms, a family-owned, federally licensed manufacturer in Greater Cincinnati, Ohio. Covered by the Faxon Lifetime Guarantee.

Faxon Lifetime Guarantee. Covers manufacturing and material defects to the original purchaser. Excludes damage from misuse, neglect, improper installation, or modifications. Finish wear from normal use is not a defect. Register your product at faxonfirearms.com/product-registration to expedite service. Full terms: faxonfirearms.com/warranty-privacy-terms.

Protected by U.S. Patent No. 12,716,670 B2. Dimensions are nominal from Faxon engineering drawings. Gas tube, roll pin, and barrel not included. Adjustable gas blocks change a rifle’s operating characteristics; always confirm reliable function with your chosen ammunition and configuration before relying on the rifle.

For questions, contact customerservice@faxonfirearms.com.