Your AR-15 probably as a gas problem, and not because it ate too many burritos either. (though if you’re feeding your rifle burritos, I don’t think the rifle is the one with a problem…)
Fortunately, it’s an easy fix and I’ll show you the best adjustable AR-15 gas blocks you can use to fix it.
So without further preface, let’s dive right in.
(NOTE: This article is part of my "Best in Class" series where I list the top choices for various parts of your AR-15. You can find the other parts here: Best in Class Articles.)
Why do I Need an Adjustable Gas Block?
The short answer is you don’t actually “need” one. The AR-15 has been working just fine for over 50 years without one. However, it’s it’s one of the better (overlooked) upgrades you can make.
An adjustable gas block can reduce recoil, increase parts life, and reduce muzzle jump, and help create world peace. (Okay, maybe not that last one.)
Let me explain.
The root of the problem is reliability with parts from a vast number of parts makers. The gun crowd hates it when things don’t go smooth. To quote Malcolm Reynolds: “It never goes smooth. How come it never goes smooth?” (And no that’s not relevant; I just haven’t quoted Firefly in way too long.)
To make a rifle function with a wide variety of parts, barrel makers need to allow for manufacturing tolerances and clearances.
Frankly, the gas port in most commercial AR-15 rifles is just too big. That’s not a manufacturing problem and I’m not saying barrel makers don’t know what they’re doing. Quite the opposite in fact. They do it on purpose
(And that’s a good thing.)
They know their barrels could be thrown into a HUGE variety of configurations. There are variables like buffer weight, Bolt Carrier Group weight, the power of the ammo, how clean the weapon is, and a few more.
So if someone has a heavy BCG, a heavy buffer, a dirty gun, and weak (read “cheap”) ammo, the weapon may not cycle. Shooters don’t like malfunctions. So from the barrel maker’s perspective, malfunctions lead to returned products, a poor reputation, lost sales and eventually bankruptcy.
Therefore, barrel makers design for the WORST possible conditions.
However, the worst possible situation doesn’t usually occur. Meaning most rifles get WAY too much gas to make sure they always function. And for the most part, it works…
But it’s not ideal.
It’s far from ideal in fact.
(But don’t blame the barrel makers. The gun world expects perfect reliability with all parts under all conditions. They deliver, but the price we pay is excess gas/power in the operating system.)
An adjustable gas block limits how much high-pressure gas from the barrel is used to cycle the action.
The result is an easy, simple and fairly cheap solution to the overgassed problem. As a bonus, you’ll get slightly reduced recoil, less weapon upset, and longer part life.
Overgassed Rifle Problems
(must… not… make… jokes…)
Overgassed rifles can malfunction because they are overgassed. It’s a case of “too much of a good thing”.
(I don’t mean to sound like Chicken Little and the sky isn’t falling. This is what can happen; but that doesn’t mean it will happen.)
For starters, in a very overgassed rifle, the bolt can unlock too soon. Not dangerously so (usually), but enough that the brass hasn’t had the micro seconds it needs to shrink back to it’s original size. If the brass hasn’t shrunk fully, it can stick to the chamber walls and cause extraction problems. (or get damaged during extraction.)
Also, early unlocking can make the rifle get dirtier faster. That’s because the high residual pressure will blow more fouling into the action.
Because the pressure is higher and the force greater, the bolt can travel backwards too fast.
This can cause a number of problems, one of which is ejection. If the bolt is traveling too fast, the brass can hit the case deflector too fast/hard. The result is the brass is thrown forward instead of of rearward. This can also damage the brass, but only reloaders care about that.
One problem that competition shooters notice is how hard the BCG hits the back of the buffer tube. On a properly gassed gun it’s barely a soft tap. (ideally the BCG will stop under spring pressure alone.) However, the BCG on an overgassed rifle will slam into the buffer tube. This increases felt recoil and can force the muzzle to move further off target.
Arguably the biggest (potential) problem is bolt speed vs magazine speed.
If the bolt is moving too fast rearward, it can “bounce” off the rear of the buffer tube and return to battery too fast. If the bolt moves too fast, the magazine spring might not push the next round up in time to chamber it.
Additionally, the action cycles more violently which wears parts faster (not typically a problem for the casual shooter). The violent operation can increase recoil and bounce the muzzle around. Not good for competition or CQB.
While all of those CAN happen, that doesn’t mean they are likely. (unless your AR-15 is REALLY overgassed.) Like I said, you probably don’t actually “need” an adjustable gas block. But they are wonderful things.
So yeah, adjustable gas blocks are REALLY good things because they can solve all of these potential problems at once.
Go technology! 🙂
How To Adjust an Adjustable Gas Block
Here are the steps.
- Turn the adjustable Gas Block’s adjustment to the completely closed position.
- Open the gas block one click (for block without clicks, a quarter turn should work)
- Load up a magazine with a single round of ammo.
- Load the weapon and fire.
- Inspect to see if the bolt locked back. If the bolt didn’t lock back, repeat steps 2-4 until the bolt locks back. Once it does, proceed to step 6
- Open the gas block one (or two) additional clicks to ensure function when the weapon is dirty or ammo is weak.
- If your gas block has a “locking screw” tighten it down to prevent the adjustment from moving
The spent brass should land around the 4 O’clock position (to your right and slightly behind) when you’ve done it correctly. My ($2400) AR-15 spits them all into a nice little pile. I could probably set a 5-gallon bucket up and catch 90% of the brass it’s so consistent.
(Hmm, I should try that the next time I go shooting. 🙂 I hate policing my brass)
The Best (Adjustable) AR-15 Gas Blocks
FYI: If you buy after clicking most of the product links on this page, I'll make a few pennies out of each dollar you spend. It's not much, but it keeps the website going and I would appreciate your support. 🙂
Don’t forget to order a gas tube roll pin when you place your order. I’ve lost them before and some gas blocks don’t come with them. For $1, it’s cheap insurance against Murphy.
SLR Rifleworks “Sentry”
In my (occasionally humble) opinion, The SLR Rifleworks Sentry is the best adjustable gas block you can buy. There might be others as good (maybe) but I’ve yet to hear of one better.
I currently have an SLR Sentry on my personal, custom-built ~$2400 AR-15. (and I have no plans to change it)
What makes it so great?
Basically, it’s better designed than the competition.
Most other adjustable gas blocks have some sort of secondary “locking set screw”, or “spring and ball” type detent to lock the adjustment in place. The SLR Sentry does it in a far better way. They don’t use a bunch of small parts and tiny balls (which can get lost) Instead, it has a larger flat leaf spring. The leaf spring provides the detent locking force to the adjustment screw.
This design is pure genius in it’s simplicity. (and I come from a family of engineers)
Another feature that’s lacking on other adjustable gas blocks is it’s adjustable from the front. For some reason, many competing designs are only adjustable from the side… which is often covered by the handguard/free float rail. Yeah, that makes no sense to me either. It’s a good thing SLR didn’t fall into this trap.
From SLR’s website:
- 100% Gas seal allows full cut off and prevents gas from fouling metering screw
- Complete disassembly is simple and takes less than 10 seconds
- NO tiny springs to corrode, break or seize / NO tiny ball to seize or get lost
Just as important, the owner (Todd) and their customer service have a stellar reputation of the “don’t care who broke it we’ll fix it” kind. If a company won’t stand behind their product and take care of their customers, I usually take my business elsewhere. Fortunately, SLR has no problems in this department.
On a more personal note, adjusting my rifle was super easy. It took less than ten minutes and has stayed where I left it. And like I said earlier, it spits all the brass into a neat little pile at my 4 o’clock. The gas block and most of the parts are 4140 steel with a melonite treatment. Many AR-15 barrels use 4140 steel and Melonite is virtually impervious to rust and corrosion.
This last point is way more important than it first appears: it’s absolutely tiny… And that’s a GOOD thing.
I left several high quality adjustable gas blocks off of this list because they are too bulky to fit under the slimmer free float rails (JP Enterprises, I’m looking at you.) Not so with this little guy. It should fit under the smallest hand guard you can find.
All said and done, the SLR Rifleworks Sentry is (in my opinion) the best adjustable AR-15 gas block money can buy.
Everything else is a compromise in my book.
Seekins Precision Adjustable Gas Block
The way I figure it, there are two types of people looking for an adjustable gas block. There are those who want the best (which we’ve already covered) and those who the best value for the money.
This one is the latter type.
The (gen 2) Seekins Precision adjustable gas block fits into the category of old reliable. I won’t pretend it’s the best in the business, but it’s a solid and dependable gas block.
Also important, it’s size. Like the SLR gas block above, this is very small. There’s nothing more frustrating than buying a brand new part and discovering it won’t fit.
That shouldn’t be an issue here.
There are two screws. One adjusts the gas flow and it’s not detent locked, so I would rotate it in quarter turn increments when adjusting it. The other screw is brass, and it’s used to “lock” the first screw down so it doesn’t move under fire.
It’s important to note the the adjustment screw faces out to the side. If you run the proper/normal length hand guard (where the hand guard ends right around the back of the gas block) it won’t be a problem. However, if you prefer the extended handguards that go past the gas block, it might cover the adjustment screw. (depending on the hand guard, you may still be able to access it). So bear in mind you might need to adjust this gas block before installing/reinstalling the handguard.
It’s easy, but something to keep in mind.
One thing to double check, make sure you get the newer “gen 2” version. The original has the brass locking screw facing to the rear, which makes it almost impossible to access with any handguard installed. The newer ones have the locking screw facing the muzzle, meaning you can get to it any time. (and yes the link points to the newer version)
At this point I feel like I should apologize.
I’ve spent half my time giving caveats for this great little guy. It really doesn’t deserve that though. Like I said before, it’s not be the Porsche or BMW of the gas block world. It’s more like a Toyota Corolla, Ford Focus, or Honda Civic. The Seekins adjustable gas block may not be flashy, but it gets the job done without costing an arm and a leg.
Fixed Front Sight Adjustable Gas Block
I don’t like fixed front sights, but I know some people do. This is for them.
JP Enterprises makes some very high quality parts. People rarely knock their quality, but occasionally complain about the price. You get what you pay for, but that doesn’t mean you need to pay a lot to get top shelf.
The JP Enterprises A2 style adjustable Gas block is exactly what the name says: It’s an adjustable gas block that looks like an A2 front sight. Nothing more, nothing less. It’s high quality (JP) but there’s nothing too fancy or flashy about it.
Personally, I prefer a good set of backup iron sights mounted to the top rail than a fixed sight. It offers more flexibility with optics and free-float rail selection and I think (subjectively) it makes the rifle look cleaner.
But if we all wanted the same thing the world would be pretty boring.
Part of the reason I waited so long to publish this article (the draft has been sitting around for months) is because it only contains two adjustable gas blocks. (Okay three, but the A2 style one almost doesn’t count.) Out of all the adjustable gas blocks on the market, it only boils down to those two?
Yeah, doesn’t seem right to me eight either.
To be sure, there are plenty of other high quality gas blocks out there. However, once you hit the $100 range, why not spend a few extra bucks and get the best? (SLR Rifleworks). And up to $80-$90 bucks, you really don’t get much more than the (gen 2) Seekins.
I’m sure you’ll tell me I missed some great gas block in the comments and you’re right. The two above are – in my opinion – “the Best”, and “best for the money.”. If you can think of another category, I’m all ears. (or eyes, since I’ll be reading it. 😉 )
Until then, enjoy some of the best AR-15 adjustable gas blocks on the market today. 🙂