Understanding Adjustable Gas Blocks and the AR-15 Gas System
One of the greatest advantages of the AR platform is its ability to change.
Upgrades and replacement parts in nearly every conceivable configuration can be ordered online, shipped to your home, and installed with relative ease.
Granted, you will want the support of a gunsmith for some of the more in-depth modifications — but in general, the AR-15 is a great platform for hobbyists and professionals to customize.
Unfortunately, it can be easy to get lost in the various options out there. As a result, you may find yourself in front of your computer at 1 a.m., staring at a web page, asking yourself “do I need an adjustable gas block?”
If that’s the case, AT3 Tactical is here to help, and we formally recommend getting some sleep.
If it’s earlier in your day, grab a cup of coffee, find a comfortable reading chair, and prepare to become a more informed shooter.
The questions we can answer here: how adjustable gas blocks work, and why they can benefit your rifle or next build.
Installing an adjustable gas block may not be necessary for your stock AR to work, but it can improve overall performance and give full control over your AR’s gas system.
The biggest benefits of the adjustable gas block are:
- Reduced recoil
- Reduced wear on components
- Reduced carbon buildup
- Eliminates the need to match the buffer weight to the gas system
- An easy adjustment for ammunition changes, use of a suppressor, and component weights without having to buy replacement parts.
Wait, What Does the Gas Block Do?
Gas from the bullet cartridge is recycled by the weapon, allowing the bolt to cycle, loading and readying the next round.
When you fire the first round, the created gas travels through a hole (gas port) in the barrel, into the gas block, through the gas tube, and back toward the bolt carrier group through the gas tube.
The gas is released from the tube into the bolt carrier group, forcing it backwards into the buffer and compressing the buffer spring.
When the pressure from the gas is no longer enough to keep the buffer spring compressed, it expands back to its normal shape and pushes the buffer forward against the bolt carrier group, putting it back into battery.
At this point, if there is another round in the magazine, the bolt carrier group will slide it into the chamber.
OK, How is an Adjustable Gas Block Different?
The gas block acts as a connector for the barrel and the gas tube, holding the tube in place and channel the gas back toward the bolt carrier group.
Traditional gas blocks have a fixed-sized hole for the gas to vent; all gas coming from the barrel will flow through.
An adjustable gas block acts not only as a connector, but also a valve for the hole the gas travels through.
That opening is widened or narrowed by tightening or loosening a screw – wider will increase the volume of gas, while narrower will limit the amount that passes through it.
Benefits/Uses: Recoil & Wear Reduction
So why does this all matter?
Well, your AR-15’s gas system should be in balance – in other words, the right amount of gas should be used to move the bolt carrier group rearward against the buffer and allow the weapon to cycle.
Unfortunately, most AR-15s come from the factory with gas blocks that allow far more gas through the tube than is necessary to cycle the bolt. This is done intentionally to ensure the rifle cycles reliably every time with a wide variety of ammunition.
But an “over-gassed” AR means has more recoil felt by the shooter and greater wear on its components. By installing an adjustable gas block, you can fine-tune how much gas is used to cycle the bolt assembly.
This helps avoid that unnecessary wear, recoil, and the carbon build-up your rifle experiences during use.
No More Playing with Buffer Weights
Traditionally, in order to lessen the wear on components, replacing the standard AR-15 buffer with heavier versions was the method used to reduce recoil, or just to allow the rifle to cycle after changes were made.
That often meant time-consuming guesswork, requiring experimentation until the correct weight was found.
An adjustable gas block makes this practice obsolete because you tailor the amount of gas to the buffer, not the other way around. A heavier buffer can still be installed – and there are still benefits to it – but either way your gas system can be harmonized with an adjustable gas block.
Over-gassing can also occur after installing a suppressor on your AR-15. A suppressor (silencer) traps gasses from the round being fired, limiting the amount of noise that exits the barrel with the bullet. When running a suppressor on your AR, it can result in more gas being redirected through the gas tube and into the bolt carrier group.
An adjustable gas block will allow you to compensate for the additional gas that a suppressor adds to your AR-15.
Pistol, Ultralight, and Alternative Caliber Builds
If you are considering an AR pistol build, an adjustable gas block can be even more important. AR pistols require heavier buffers, which impacts the amount of gas needed to fully cycle the weapon.
As mentioned, changing buffer weights will affect the entire gas system, and any imbalances can create issues that would require an adjustment to the gas system.
Similarly, changes in the caliber of the weapon (i.e. from 5.56 to 9mm, 6.5 Grendel, etc) or swapping out factory parts with lighter components may also necessitate tuning of the gas system, in order for the gun to reliably function.
When Adjustable Gas Blocks don’t help
If you are having difficulty getting your rifle to cycle properly, an adjustable gas block doesn’t solve every problem that can occur.
For instance, if your rifle is “under-gassed” — it means that the gas system doesn’t send enough gas to move the bolt carrier group properly. And involving a valve in the gas system doesn’t create more gas to solve the issue – it’s only a device used to reduce the amount of gas harnessed by the system.
The typical causes of under-gassing include:
- A misalignment of the gas tube and gas block.
- A loose or damaged “gas key”, which is the part of the bolt carrier group that receives the gas from the gas tube.
- Bolt gas rings that are either damaged or missing.
- Excessive buildup of carbon or lubricant within the system.
- Underpowered or defective ammunition.
If this is happening to you, here are some simple troubleshooting steps to take:
- Double-check your rifle to ensure that the components:
- are installed and aligned correctly
- aren’t missing any parts
- Disassemble and clean the rifle as thoroughly as possible.
- Try a different brand or type of ammunition.
If you are still experiencing a problem after all of this, you should take your rifle to a gunsmith and have them diagnose the issue.
Tuning the Gas System
Once you have installed an adjustable gas block on the barrel, tuning it is an easy process.
For a complete rundown, check out our full article “Installing and Tuning Your Adjustable Gas Block,” but the short version is this:
- Fully tighten the gas screw to close off all gas from the system.
- Insert a magazine with a single round in it, chamber the round, and fire it – the bolt should not lock back on the empty magazine.
- Loosen the gas screw by one complete turn.
- Repeat steps 2 and 3 until the bolt does lock back on an empty magazine.
- Loosen the gas screw another half-to-full turn and lock it in place.
- Test fire repeatedly with different ammunition types to ensure smooth, consistent function.
Downside to Adjustable Gas Blocks
The only real downside to the adjustable gas block is cost, as well as the effort needed to install and tune.
Many run upwards of $75 per unit, which may discourage some buyers who aren’t fully convinced that they need one.
Fortunately, there is an answer for those people — and for those who know they need an adjustable gas block.
Wojtek Weaponry makes a quality adjustable gas block for just under $40 which AT3 Tactical recommends and carries (you can order one here).
Otherwise, we encourage you to browse other manufacturers’ products with confidence, knowing more about one of the most important purchases you can make to optimize your AR-15.
One Last Tip
If there’s anyone that knows the AR-15 platform, it’s the US military. As a special offer for our readers, you can get the Official US Army Manual for AR-15/M4/M16 right now – for free. Click here to snag a copy.