What if I told you one part could reduce your AR-15 rifle’s recoil, reduce wear, and even open up a wide variety of customization options?
Sound too good to be true?
It’s not, I promise.
Through an adjustable gas block, all this is possible.
An adjustable gas block offers a variety of advantages over a standard block. Today we are going to go over those advantages, how to choose an adjustable gas block, and how to tune one.
Here are our top picks:
|Best Low-Profile:||Superlative Arms|
|Best Fixed Sight:||JP Adjustable|
|Most Affordable:||Seekins Block|
*Updated 2018*: More info on tuning and models
Table of Contents
Why Bother with an Adjustable Gas Block?
It’s important to understand how direct impingement works to understand the value of an adjustable gas block.
Direct impingement works by taking advantage of the gasses produced by burning gunpowder to cycle the rifle. The gas propels the projectile downrange and as it travels through the barrel a bit of that gas is bled off.
The gas goes through a port on the barrel, into the gas block (the bit we’re talking about today), and down the gas tube.
The gas goes back into the receiver, pushes the bolt rearward, which extracts and ejects the round. It strikes the buffer which compresses a spring and sends the entire system forward after the spring hits its apex.
This entire system of operation relies on gas, and therefore the gas system becomes incredibly important.
The gas system is composed of the gas block and gas tube. There isn’t much you can do with a gas tube, it’s an aluminum tube and the way it affects the rifle is generally tied to its length.
The gas block, however, is what bleeds the gas from the round to the gas tube. The gas block can be adjusted or swapped out entirely to create a variety of changes in the rifle.
A fixed gas block allows a set amount of gas to flow through the system. This is basically a one size fits all approach for rifles.
It doesn’t take into effect different types of ammunition, suppressor use, buffer weight, or BCG weight (and how many BCGs have vastly different weights).
On the other hand, an adjustable block can be tuned to help you get the most out of your rifle build and to get all your parts working together a little more efficiently.
Tune Your Gas Block
An adjustable gas block is designed to allow you to fine tune the gas needed to run the system.
This allows shooters to tune their rifle for different ammunition types, for different weight internals, and of course suppressor use.
Most rifles are actually over-gassed, meaning more gas flows through the system than necessary.
Is this a bad thing?
I mean it’s not the kind of gas you pay by the gallon for right? Well, there are a few issues with over-gassed rifles.
First, you are actually getting more recoil. More gas flowing rearwards means more force, and more force means more felt recoil.
This can even be true if you’re rocking the very best lightweight bolt carrier group.
Recoil makes for a harder to control gun, which degrades your accuracy.
An over-gassed gun is also going to run hotter and dirtier. And not the fun kind of hotter and dirtier, either.
The extra gas and debris are going to raise the internal temperature and create a much dirtier gun.
That extra carbon build up makes the rifle less reliable and increases the likelihood you’ll get a failure-to-fire or failure-to-feed issue.
Next, we should focus on wear. Over-gassing has also been tied to locking lugs wearing out well before their time is up.
The fact the bolt is being shot backward with excess force could result in a loosened gas key over time as well.
When to Crank Up the Gas
To be completely fair there is a time for over-gassing. When a rifle has been run hard, is filthy dirty, full of carbon and sand, and moon dust – then you need that extra gas.
That extra gas keeps everything moving when the inside of your gun looks like a dirty litter box. With an adjustable gas block when things get wicked, simply open the gas block up and let it flow.
Most adjustable gas blocks are designed to be used with a simple key to adjust the system. These adjustment areas are easy to access, even with a rail system over the gas block.
Recapping the Benefits of an Adjustable Gas Block
An Adjustable Gas Block solves the following problems
- Overgassing your rifle.
- Reduces recoil.
- Reduces wear and tear.
- Makes your rifle run cleaner and cooler.
- Let’s your rifle run more reliably when full of carbon fouling, sand, moon dust and
the blood of your enemiesother debris.
How to Choose an Adjustable Gas Block
You choose an adjustable gas block the same way you choose most parts for your rifle. You choose based on both your preferences and needs (and price, most of the time).
There are actually a wide variety of different options when it comes to adjustable gas blocks.
Like regular gas blocks, adjustable gas blocks come in a variety of different sizes. You have the standard .750 for your normal medium profile barrel, and .875 for those special snowflake barrels.
We also have .936 for heavy bull barrels, and .625 for pencil barrels.
You’ll need to know the barrel profile you want, or you have, before choosing an adjustable gas block. One note is that an adjustable gas block allows you make a very lightweight rifle, and a pencil barrel is beneficial to this.
Types of Adjustable Gas Block
Personally, I really like a fixed front sight. Something about the stability and simplicity really appeals to me.
As a Marine, I’m quite used to the A-frame style fixed front sight and I like it. This, unfortunately, means I really can’t use a free floating rail system.
My choices for full-length rail systems are also limited depending on where my front sight is fixed on the barrel.
A free floating rail system can help with the overall mechanical accuracy of a rifle, and to run a free floating rail system I am going to need to run a low profile gas block.
A low pro gas block disappears underneath a rail system. These low profile gas blocks allow the user to utilize a longer rail system that could extend all the way up to the muzzle device.
These rails are popular with those using the C-Clamp style of shooting like you’ll see in most competitive shooting matches.
There are also railed gas blocks. These gas blocks are basically low profile gas blocks with a Picatinny rail installed on it. This system is excellent if you have a set of detachable flip up iron sight you’d like to use.
For example, I love my XS Troy CSAT AR sights, so with a railed gas block, I can equip these night sights on my gas block.
Now what about clamp or set screws? I personally like clamps since they probably more evenly distribute the stress onto the barrel. But if you really want to make sure your block doesn’t move…dimple your barrel (if it isn’t already) and get the set screws.
How to Tune an Adjustable Gas Block
So this is a very simple process. Depending on your gas block and rail system you may want to leave the rail uninstalled.
This sounds crazy but you have to be able to adjust the gas block. Wear some gloves, and hold the mag well.
Accuracy isn’t the major issue here so a solid shooting position isn’t needed. If you can reach your gas block and adjust it with the rail system in place then do so.
Grab the load you plan to shoot the most through your rifle, or the load that will be most important in your rifle.
For example, if you hunt with your AR 15 you want to tune the rifle to your hunting ammo, and not your plinking ammo.
Hiccups while plinking isn’t an issue, hiccups while hunting can be.
Make sure you know which way opens and which way restricts gas flow. I would start with it opened to allow maximum pressure.
Load a magazine with one solitary round and test how it cycles. You are looking for two things, how reliably the round cycles the action and if the bolt locks to the rear with an empty magazine.
If the weapon cycles perfectly and the bolt locks to the rear restrict the gas flow by a ½ turn of the adjustment screw.
Repeat loading one round per magazine and firing, observing cycling and the bolt locking to the rear. Restrict the gas system another ½ turn.
Rinse and repeat until the bolt does not lock backward on an empty magazine. At that point open the gas system ¼ turn. Repeat the test.
If it locks back that is your optimal gas setting.
If the bolt still fails to lock to the rear open adjust the system another ¼ turn, and this is your optimal setting.
Run a magazine through the weapon and ensure it cycles reliably.
At this setting, the rifle will cycle with the least amount of recoil, and place the least amount of wear and tear on your internals (and your shoulder).
And now the part you’ve all been waiting for (or the part you skipped straight to): our recommendations.
Best Fixed Sight Adjustable Gas Block
Fixed Front Sight Adjustable Gas Blocks are simple, robust, and provide a solid front sight option.
Suggested Fixed Sight option: JP Enterprises Adjustable Gas Block with A2 Front Sight
This is just an upgraded version of the standard A2 style front sight that has served the military for generations. It’s well made, rock-solid in design, and co-witnesses perfectly with most other optics.
Best Low-Profile Adjustable Gas Block
Low profile adjustable gas blocks allow the use of full-length handguards and free-floating rail systems. They are tiny little things that disappear under a rail system.
This adjustable gas block also offers a bleed off hole to reduce gas blowback when rocking a suppressor.
Be sure to check out our complete Superlative Arms Adjustable Gas Block review as well!
And the previous gold standard…Seekins’ Adjustable Gas Block for a more affordable option. It’s what I used to run in previous rifles but sometimes my handguard configuration wouldn’t let me reach the gas detent. Plus…it doesn’t have the bleedoff option. But if you’re looking for a plain Jane block that works…the Seekins is great.
Best Picatinny Railed Adjustable Gas Block
Picatinny Railed Gas Blocks allow you to utilize any front sight that’ll attach to a Picatinny rail.
Suggested Picatinny Railed Option – Double Star Pic rail adjustable gas block
Take this Block and Adjust It
An Adjustable gas block is slightly more expensive than a regular gas block, but it does so much more.
This is one of the most important parts of your rifle. I don’t think it will be long until adjustable gas blocks will the be standard among manufacturers.
Speaking of accessories that should be standard, you need a red dot or optic. Our list of Best AR-15 Optics & Scopes will help you find what is right for you.
What do you think? Was this helpful in your quest to find the perfect gas block? Let us know down below in the comments.