Most of us - at least in the early stages of our relationship with the AR-15 - go through the same upgrade process. First thing is to mount an new sight or red dot. Then we upgrade it with a buttstock that would ideally suit us.
After some time has lapsed, we start to look for a better trigger and customized upper receiver. Usually near the bottom of the, too often overlooked, is the gas block. The gas block paired with the gas tube is a part of a system that is the most underappreciated contributor to a gun's performance and reliability.
The Purpose of the Gas Block
The gas block is the component that straddles the barrel and fits over the gas port. It manages the flow of hot gas through the gas hole down to the gas tube and further on to the head of the bolt carrier.
The AR-15 has been operating “just fine” for over 50 years utilizing a direct impingement gas operating system. While the AR platform has been constantly modified and improved over time, the typical factory version has stayed pinned onto the barrel.
Known as a fixed front sight gas block, these simple and robust devices transfer a fixed amount of hot gas through the tube back into to the bolt carrier group to cycle the action. In most AR-type rifles, the fixed models provide more gas than is needed. This causes more recoil and increased wear on parts. And that means an over-gassed rifle runs hotter and dirtier.
What is an Adjustable Gas Block?
The industry soon realized that this simple but the critical component could be improved by adding a small metering screw on the side of the gas block. Furthermore, the best contemporary adjustable ones on AR-15s are modernized with spring-loaded detents that lock the set gas flow in place. Audible clicks help identify the setting.
This concept of an adjustable-gas system can be vividly explained as a valve that regulates how much hot gas is directed back into the upper receiver. Unlike the standard philosophy that “one size fits all”, the adjustable gas block is designed to allow reliable use of different kinds of ammunition. It also allows for suppressor use or upgrading your rifle by helping adjust the weight.
An AR-15 with an adjustable gas block will decrease felt recoil, resulting in a faster follow-up shot. It will put less stress on the operating parts. And due to the lower carbon build-up, your rifle will run cleaner and cooler.
Ultimately, when you add gas-tuning devices, your system will operate more smoothly and muzzle rise would be reduced. That means you also get a more accurate shot..
As a critical link in the chain, this component needs to be constructed from quality and durable materials like carbon steel, stainless steel or even titanium. All of them have their benefits and risks. Carbon steel is prone to rust; stainless steel is harder to machine. Titanium is approximately 40% lighter than steel, making it an excellent option for AR-15 gas blocks. But it is much more expensive and difficult to machine than the other options.
Considerations For Your Gas Block
As you might suppose, manufacturers offer these in appropriate sizes for your barrel. Most adjustable gas blocks are designed to be used with a typical medium profile barrel with a diameter of .750″. However, there are also gas blocks for .936 diameter heavy bull barrels. The .625 diameter is another common size for pencil-profile barrels.
To ensure your AR runs reliably, you also have to purchase a gas tube of the correct length. Of course, you can always just keep your old one, too.
Besides the size, you should notice the different methods for attaching a gas block to the barrel. One type clamps on, but the most common mounting type is by slipping the block down the barrel and fixing it in place by setscrews on the underside.
If you are plan on installing a free-float handguard to enhance the overall mechanical accuracy of your black rifle, then a low-profile gas block is a must. These are compact and they disappear underneath long free-float handguard and its rail system. As you can imagine, they let you mount a longer rail system and allow more space for accessories.
Some gas blocks feature Picatinny rail installed on top of them, making a perfect platform to mount a set of detachable flip-up iron sights.
Quick Comparison Chart of the Top Gas Blocks for the AR-15
SGB Geissele Super Gas Block
ODIN Works Inc. AR-15 Low Profile Gas Block
J P Enterprises - AR-15/M16 Adjustable Gas Blocks
VLTOR Weapon Systems - Ar-15 Gas Block Low Profile
Superlative Arms Llc - Ar-15 Adjustable Gas Block .750" Clamp On
Reviews of the Best Gas Blocks for the AR-15
In this guide, we’ll suggest the best AR-15 gas blocks in several formats, including small low-profile units with lock screws that disappear under a rail system, ones with rails on top of the gas block, and one that clamps on the barrel.
When we are talking about triggers, most of us have heard about the quality of Geissele products. But Bill Geissele’s company also offers this great non-adjustable and low-profile gas block made of 17-4 stainless steel. The Geissele Super Gas Block (SGB) is the lightweight low-profile model intended to tightly fit around a .750-inch diameter barrel found on most AR-15 and M4 Carbine firearms.
The SGB has two possible mounting solutions, a standard one for the casual and target shooter, and a “bomb-proof” installation. The latter designed for duty weapons and combat situations and adds a completely new level of security. While everyone can do the first type of fastening an SGB to the rifle barrel, the “bombproof installation” requires at least an advanced hobbyist with a drill press, if not an experienced gunsmith.
On the negative side, we’ve found some issues with a tight fit on stainless barrels. Also, this blocks don't fit all rail systems since Geissele`s profile is slightly larger than other low-profile gas blocks.
The ODIN Works adjustable gas block is manufactured from carbon steel and superalloys - called Inconel - resistant to high pressure and heat. It was born out of their experience in the aerospace industry.
This version utilizes a front-facing Inconel adjustment screw and spring to ensure the proper functioning of the gas system. Featuring 20 adjustment points, the ODIN Works rifle gas block can be tuned for silencer usage or weak/hot loads.
The ODIN Works gas block fits .750″ diameter barrels and can be installed as easily as any other low-profile type. It is secured to the barrel with two setscrews on the lower side. However, if you do not want to dimple the barrel, there is also a clamp-on version available.
American manufacturer JP Enterprises is targeted toward the competitive shooter market. AR components from JP indeed offer competition-quality adjustable gas blocks.
JP Enterprises produce theirs from lightweight 6061 T6 aluminum or rugged 416 stainless steel for additional muzzle weight. They are intended to mount underneath many handguards on the market. Along with a standard clamp-on design, there is a two-piece model that allows for easier installation on barrels with pin-and-weld muzzle devices.
The JP "clamp style" model is attached with four hex-head setscrews instead of the usual two. Still, to clamp the block securely to the barrel you need to add some Loctite on each screw.
The JP Adjustable Gas System offers easy access to the side gas adjustment and internally retained detent components. That means you will have no more the lost parts.
Since JP gas blocks are much bigger than other low-profile blocks, they require you to choose a shorter handguard. But you’ll still be able to attach accessories to the rails. Just be careful of the dimensions because the gas adjustment screw, when backed out, interferes with some handguards.
The VLTOR non-adjustable gas block is a slim replacement for the cumbersome and classic fixed-sight tower models. It presents a carefully-assembled gas management system.
The popular VLTOR low-profile models are tiny and compact, keeping weight down. They’re an ideal choice for the ultralight build or when using a handguard that is mounted over the whole gas system.
Besides fitting the .750” diameter of standard barrels, this one is also made to fit lightweight barrels that feature a .625" diameter, commonly referred to as "pencil" barrels.
These are machined from 17-4PH stainless steel and 4140 carbon steel. They come in stainless steel or matte black phosphate finishes.
The VLTOR low-profile gas block is available in two different methods of attachment. You can elect for the more conventional screw-on option with setscrews at the bottom, or a clamp-on model that squeeze around the barrel.
Note that clamp-on models will not fit under an exposed bottom rail channel on the inside of the handguard.
There’s also one aesthetic negative. Because it covers only one inch of the barrel's surface, after removing a regular front sight post you will have silver taper pin hole showing where the front sight post was.
It was the only a matter of time until someone would merge several gas-system functions into one. The Superlative Arms did it with its 3-In-1 Gas Block.
This SA device has united three different types, providing you with the performance of a standard non-adjustable, a restrictive adjustable gas block and their newly- patented “bleed off” gas block.
Unlike other adjustable gun blocks, this model in "Bleed Off" mode will bleed the excess gas out from the front of the gas block. When using the bleed-off setting, you can tune your rifle to the peculiarities of the ammo and the rifle. Above all, you also get a perfect component if you are running a suppressor or are using a pencil barrel.
This innovative design allows the rifle to shoot more softly and cleanly because adjustment detent is placed outside of the block and therefore there is no contamination.
This gas block is a bit tall and limits your options for handguards. At the same time, the bleed-off might work better with a longer gas system instead of the high pressures with pistol length. While being a great system, some adaptations in this area would be helpful.
How to Install Your New Gas Block
For people familiar with AR builds, installing this upgrade is a relatively easy and straightforward operation that requires only the usual household tools.
- Remove flash hider from your barrel muzzle and forward handguard.
- Using a hammer and punch, unpin the factory gas block and remove it from the barrel.
- Install your new gas block using set screws or clamping screws to lock it into place. If you are dealing with an adjustable gas block, you might need to adjust the new gas block before reinstalling the handguard. Some of them have the locking screw in a location that makes it almost impossible to access with a handguard installed
- Reinstall your handguard and muzzle device. However, prior to that final move, in case.
If you are unfamiliar with tools and basic-level gunsmithing, you can easily find a reputable gunsmith to do this inexpensive gunsmithing job for you.
Aftermarket low-profile gas blocks make a huge difference in shooting comfort. They enable you to shoot faster and at the same time reduce fatigue on your firearm. They also prolong the time between cleanings and cause heat reduction at the bolt.
That makes them one of the best upgrades you can make especially if you plan to use a specific type of ammunition, handloaded ammo, or simply you want to mount any kind of suppressor.
Although adjustable gas blocks require more time for tuning, we strongly encourage this upgrade as the most significant performance improvement anyone can make to his or her AR-format rifle.
More reading: AR-15 Gas Piston Buyers Guide