How to Install a Gas Block on an AR-15

Posted by Faxon Firearms Staff on Feb 20th 2023

How to Install a Gas Block on an AR-15

The AR-15 Gas Block is an often-overlooked component that can have a huge impact on the overall performance of the rifle. It allows for gas to escape the barrel in a controlled way before the round leaves the muzzle.

This escaping gas is what allows for the action to cycle automatically.

The expanding combustion gasses are released through a hole in the barrel called the gas port, are captured by the gas block, travel down the gas tube, and then push the bolt carrier group to the rear where it ejects the spent casing.

This makes the gas block extremely vital to the reliable function of your AR-15 and definitely puts it into a class of parts that you shouldn’t overlook.

A poorly made gas block can cause the rifle to not cycle properly by releasing too much or too little gas through the gas port. A quality gas block keeps your rifle running reliably, and a really good one will even let you manually tune the rifle to get better performance and even greater reliability.

Look for an adjustable gas block if you want to get the most out of your rifle, especially if you might run it with a suppressor.

Different Types of Gas Blocks

Besides adjustable and fixed gas blocks, there are a few different styles to be aware of. These can be adjustable or fixed. Adjustable gas blocks are great, but you don’t necessarily need them if you’re willing to tune the buffer tube spring and buffer itself to get the perfect setup.

Clamp-On

First, we have what used to be the most common design, the simple clamp-on gas block. These blocks clamp around the barrel and tighten down using set screws to hold themselves in place.

These are generally not recommended these days as they tend to leak gas, which can be a problem for both reliability and cleaning. It’s also really easy to sheer off the delicate set-screws while trying to get them tightened down securely.

Low-Profile

If you need a gas block that will fit under a handguard, then you need a low-profile gas block. These are specifically designed to fit underneath a standard or free-float handguard, allowing you to have a full-length handguard that ends closer to the muzzle, regardless of barrel length, and fully protects your gas system.

These gas blocks are pretty much the standard these days, and almost no factory rifles are coming off the line with anything else on them. If you’re not chasing a certain look, this is what you should go with.

Most of them are a little easier to install, and they’re more likely to be adjustable to boot.

Triangle Front Sight Post + Gas Block Combo.

This style of gas block, often called an A2-style front post though there are others, offers an old-school triangular front sight post that doubles as a gas block.

These aren’t all that popular anymore unless you’re building a clone of a specific service rifle, or you just really like the look. They can make mounting certain handguards impossible, aren’t adjustable usually (though some high-end models are), and interfere with certain modern optics like LPVOs.

If you have a retro-style rifle with a delta ring assembly and non-free-float plastic or wooden handguard, this might be what you want to go with though, and there’s nothing wrong with them.

How to Install a Gas Block

*Note: insure that your barrel’s gas block journal matches the size gas block you purchase. Different barrels have different journal sizes, so a bull barrel is going to be different than a pencil barrel.

Once you’ve chosen your gas block, preferably a low-profile adjustable model if this is your first time building or upgrading your rifle, here’s what you’ll need. We include instructions for installing a gas tube to one of our pinned gas block barrels, though your barrel may not have the pin cutout for this.

If you have a barrel without this pin cutout, you can skip step 7 in the step-by-step, and leave out the 5/32” roll pin punch listed in the tools section below.

We generally recommend going with a pinned gas block if you can, however, as it’s a much more secure method of mounting the block to the barrel. Gas blocks get very hot under extended fire, which causes the metal to expand, which can lead to the block working its way loose, or starting to leak, which can cause a host of issues, including dwell time problems.

A pinned gas block can’t walk out under pressure or shift during thermal cycles, making it a more secure overall choice.

If you don’t go with a pinned gas block barrel, our non-pinned gas blocks feature a third set screw to help ensure they have the lowest chance possible of sliding under heavy use.

Necessary Tools

Small roll pin punches in 5/32” and 3/32” (the same ones you’ll need for a lower receiver build)
Brass or polymer-headed gunsmithing hammer (polymer recommended, you don’t need an expensive one)
Set of Allen keys
Torque wrench
High-heat thread locker
Benchtop vise and non-marring receiver clamps/jaws (not technically required, but highly recommended)
Needlenose pliers with serrated jaws (optional, recommended to save your fingers if you miss with the hammer)
Gas tube alignment tool (optional again, still highly recommended)
Your favorite CLP + maybe some WD-40 or other degreaser
Barrel nut wrench/Armorer’s wrench (For barrel nut/lock ring if you’re removing or reinstalling a barrel)
Molybdenum sulfide grease with no metallic additives for the receiver’s threads and barrel nut threads if you’re remounting the barrel after. Stainless steel and aluminum don’t like to pair up without a good grease.

Necessary Parts

Gas block w/ taper pin + screws
Gas tube w/ roll pin
Upper Receiver with attached barrel and barrel extension

Installing Your New Gas Block

Once you have all your parts together, it’s time to assemble everything. We’re going to go over this as if you’re installing a modern low-profile gas block, rather than an A2-style front post as that’s a little different, though still more or less the same process.

We’re also going to assume that the barrel is already attached to the receiver and that you have the manufacturer’s instructions for removing your handguard. Read through all the steps first so you have an idea of what you’ll need, and when you’ll need it.

With the handguard off and the receiver or barrel clamped horizontally in your vise, clean and degrease your barrel, gas tube, and the inside surfaces of the gas block. This will give us nice clean contact surfaces to work with. If you have all new parts, then just a little degreasing of the barrel and lubing of the gas tube hole on your gas block will suffice.
Insert the end of the gas tube with the hole for the roll pin into the gas block with the roll pin hole in the tube lined up with the roll pin hole in the block. Push the tube into the block until the two holes align. It may take a small amount of pressure, but it shouldn’t take a lot. Try again with more lube if you feel like it’s too much of a tight fit.
Use the 3/32” punch to seat the smaller pin through the gas tube hole, locking the gas tube to the block. Use the pliers to partially seat the pin first by tapping it directly, and then switch to using the punch. Go slowly, and make sure that you’re holding the punch at a 90-degree angle to the block.
Once this is lined up, slide the gas block over the barrel, and allow the other end of your gas tube to slide into the corresponding hole in the receiver.
Apply a small amount of high-heat semi-permanent thread locker to the set screws included with your gas block.
Use an Allen wrench to thread in the set-screws that hold your gas block to the barrel, checking that the large roll pin hole in the block is aligned with the appropriate cut-out in the barrel. These two holes are perpendicular to the set screws and should be easy to spot.
For the next step, use the gas tube alignment tool to double-check the alignment of the gas tube with your receiver as you proceed with step 5. If you didn’t buy the alignment tool, install your rifle’s bolt carrier group and charging handle into the receiver and use the handle and gas key on the BCG to check the alignment
Use the 5/32” punch to drive the larger of the two gas block roll pins through the hole in the gas block and out the other side. We recommend starting by holding the pin with the needlenose pliers and hitting it directly until it is partially seated, and then switching to the punch to finish setting it. The pin should protrude by the same amount on each side of the block.
Once the pin is in place (or you’ve skipped the preceding step because you don’t have a pinned gas block barrel) use your torque wrench to tighten the screws to the manufacturer’s specs or 30-40 in/lbs at most if you don’t have torque specs, tightening each gradually and in smallish increments until you reach the required torque.
Install your handguard nut, handguard, and flash hider/muzzle device according to factory specifications, and enjoy your new gas block!

The Faxon Firearms Difference

Low-quality gas blocks and barrels can dramatically lower the performance and reliability of your rifle. At Faxon Firearms, we pride ourselves on making high-performance parts that shooters can count on, no matter what.

Our gas blocks are precision machined and work phenomenally well with our barrels, as well as with any other quality barrel. Unlike other brands, our blocks use three precision-machined set screws to ensure secure fitment for the life of your rifle, no matter how much you shoot.

We also have pinned gas block barrels available that offer the most secure method of mounting your gas block. These barrels lock your gas block in place with a roll pin to keep them from working loose due to heat expansion under extended firing.

Whether you buy a complete Faxon setup from barrel to block to tube, or you’re just adding one of our gas blocks to an existing setup, you can rest assured that we’ve taken every bit of care with your new parts that we do when building our own rifles.

And as always, each of our American-made barrels for the AR-15 platform, AR 10 platform, or handguns are backed by the Faxon Lifetime Guarantee.