Wednesday, November 25, 2020

Tame that Gas! Improving the Direct Gas Impingement (DGI) Tactical AR-15 Rifle/Carbine at Relatively Low Cost

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By Jeff Gurwitch

July 7, 2020

The M4//M4A1/M16/AR-15 has proven to be one hell of a rifle/carbine. I’ve carried it with total confidence, and have employed it pretty successfully during my many tours overseas with U.S. Army Special Forces. The inline design and low height above bore still put it ahead of just about every military rifle that’s come out in the last 10 years or so, including the SCAR, Beretta ARX-160, and CZ 805 Bren S1, just to name a few.

Does this mean there’s no room for improvement with the AR? Of course not. The fact is, most ARs are slightly over-gassed for reliability, which is fine, unless of course one runs suppressed a lot (like most of Special Operations now does), or if you run hot ammo (like all the U.S. Army does with M855A1)…or if you’re like me, and just want a rifle that has even softer recoil, allowing faster shooting, while maintaining accuracy.

So, what can be changed? Well, how about adding adjustability to the AR’s direct impingement (DI) gas system. Being able to adjust the AR’s gas pressure will allow one to tune the rifle to proper pressures when running suppressed. Plus, it’ll also address the issue of increased pressure from gas port erosion. Even if your AR is gassed correctly, over time, via shooting, the gas port hole will erode from the inside, allowing higher pressures into the gun.


Three uppers I’ve converted to adjustable gas using BPM’s Accu-Set Adjustable Gas tubes. The rifle at top is going on over a year and a few thousand rounds since installing one. Thus far, super reliable. And, thanks to the adjustable gas tube, very soft shooting.

This of course means a harder-cycling action on the moving parts, which can lead to increased wear on bolt lugs, the extractor, and other parts. Having the ability to dial the gas back down would not only increase service life of parts in the AR, but also allow one to tame excessive recoil from over-gassing. What I’m suggesting is of course nothing new. Adjustable gas blocks have been on the market for quite some time now. What’s changed is improvements in adjustable gas technology.

10 years ago, if you asked me if adjustable gas blocks were a worthy item, I’d have said “no”, mainly because most early designs relied on a screw that one turned in or out to adjust gas. Then, once the desired pressure was set, you would then need to apply thread locker to keep it in place. Or, it relied on another set screw to hold in place. This of course meant they were not truly adjustable in terms of being able to adjust on the go, since the setting was thread-locked in place–not to mention you’re relying solely on a turn screw to stay in place while being exposed to high heat and pressure from shooting, with nothing more than thread locker to keep it in place.

Not exactly the most confidence-inspiring set-up. While suitable for range work and shooting matches, I would not have recommended these adjustable gas blocks for any real-world tactical/combat shooting applications.

So why trust adjustable gas systems now?

In short, technology has vastly improved. Specifically, most adjustable gas systems available now have positive click adjustments. This means that not only is there no need to worry about adjustment screws backing out, but you can also set or change gas settings on the fly, depending on how your rifle is set up.

Having positive click adjustments means you can have a certain number of clicks when running suppressed, then a different number, or different lever position for running unsuppressed, depending on the design. Or, if one wants to be able to tune their rifle to a specific type of ammo, they can then have a different setting for other types. That’s all possible now.
“If it aint broke don’t fix it” is the response by many in online gun forums anytime the discussion on the validity of DI adjustable gas comes up. The concern expressed by many is why introduce another point of failure into the system. My answer to this is that in many other gun designs, having an adjustable gas system has already proven to be reliable and offer a benefit to the user. Rifles like the battle-proven FN FAL and the HK416 have adjustable gas capability, so why not a DGI (Direct Gas Impingement) AR?


Adjustable gas on rifles is nothing new. The battle-proven classic FN FAL has always had the capability to change gas pressures. (Photo credit: military.wikia.org)


Close-up of the rotary-style turn knob on the FAL’s gas block. You can see by the size of the different holes that adjusting it increases or decreases the amount of gas allowed to exit the gas block. (Photo credit: northwestfirearms.com)

The FN FAL’s adjustable gas settings are meant to be used when the rifle gets dirty and needs a plus-up in gas to maintain reliability. The HK416A5 adjustable gas system was designed with running suppressed in mind, so one could keep the correct gas pressure while shooting suppressed.

Of course many will point out that these are piston rifles, so they’re not the same as DI/DGI guns, and that with said DI/DGI guns, you’re just introducing another failure point. I find this argument to be nonsensical. The reality is, the only difference is that with a piston gun, gas blows against some sort of op rod (operating rod), and with DI, gas blows directly against/into the bolt carrier. So, how is it that an adjustable gas option is somehow going to be automatically unreliable in a DI gun?


Close-up of an HK416 gas block. Note the gas adjustment lever on the side. Even a simple, suppressed or unsuppressed option is better than just straight gas. (Photo credit: hkpro.com)

The short answer? It’s not. This is of course dependent on the design of the adjustable gas system (hence my distrust in just turn screws and thread locker). However, today there are many solid designs out there that can add a capability and benefit to the AR. What are some of them? Let’s take a look.

Modern Improvements to DI

I covered one method of adjusting gas in the AR previously on DR, the Barnes Precision Machine (BPM) Accu-Set adjustable gas tube, back in December of 2018. It is a gas tube that has a built-in regulator with positive click adjustments, allowing one to change the amount of gas flow through the gas tube. Having run one for over a year now in one of my main ARs, I’ve found it completely reliable so far. In fact, I’ve gone ahead and installed BPM Accu-Set gas tubes in all three of my DI uppers that I own.

Being able to set the gas to where I have minimal felt recoil equals faster follow-up shots while still maintaining 100% reliability. At only $60 for the adjustable gas tube alone, it’s also the cheapest method to convert your AR to an adjustable gas system.


Close-up of a Barnes Precision Accu-Set Adjustable Gas Tube. Via an Allen wrench, you can turn up or down the amount of gas allowed through the tube.

Next up is one item that, although I haven’t tried it yet, looks super interesting, and that’s the Bootleg Four Position Adjustable Carrier, from Bootleg Inc. In this case, the gas flow appears to be able to be changed in the carrier after it passes through the gas key, with the adjustment point being how much gas is allowed to vent out and actuate the bolt unlocking.

It has four settings that can be adjusted on the fly via a flat-tip screwdriver slot built into the side of the carrier. This looks to be a very solid design, and one that I’d love to try sometime. Price-wise, it’s not bad at $179.99 for a complete carrier. That’s inline with prices for high-end carriers with nickel-boron coatings or other features above MILSPEC.


Bootleg Four Position Adjustable Carrier. By using a flathead screwdriver, one adjusts through four positions for gas pressure. Looks to be a very solid design, and one I’d love to try. (Photo credit: bootleginc.com)

For an adjustable gas block, the Seekins Precision Select Adjustable Gas Block looks to be a very solid design, and another one I’d love to try. Built into the top of the gas block is a lever with positive click adjustments, allowing one to regulate how much gas flows into the gas tube.

I like the idea of having a lever one can move by hand. Both the BPM gas tube and Bootleg carrier require a tool (Allen wrench for BPM, and flat-tip for Bootleg carrier). The front of the gas block is marked with plus and minus marks, so there’s no confusion as to which direction one needs to go to add or reduce gas pressure. At $119.00 USD cost isn’t bad for what you’re getting.


For those wanting an adjustable gas block, Seekins Precision’s Select Adjustable Gas Block looks like a winner. Positive click adjustment to the correct amount of gas can be made via the large lever on top. (Photo credit: seekinsprecision.com)

Which one should you choose?

Which is best? That depends. All three of these products do the same thing, allow for adjustable gas. The differences are where the gas adjustment point is, ease of installing, ease of adjusting, and cost. The Bootleg carrier is the easiest to install, but is also the costliest of the three. The BPM Accu-Set gas tube is the next-easiest to install, and the cheapest method.

However, to be able to have access to adjust the gas on the fly, there needs to be a hole in the top of the hand guard. If there isn’t one there already, a hole will have to be drilled if you want to be able to adjust the gas pressure after initial installation and test fire. I know that for some, this will be a showstopper, for they don’t want a hole in their handguard. For me, it’s no big deal, but BPM does offer handguards with holes that line up to any gas length, along with installation services with your existing handguard.

The Seekins Precision Select Adjustable Gas Block is the most complicated to install compared to the other two, but the price, again, isn’t bad. It all depends on one’s priorities based on ease of install ation, cost, and which item they think will work best for their AR. Of course, having used a BPM ACCU-Set gas tube for over a year now with zero issues, it gets my vote.

But that doesn’t mean I’m counting the other two out. Both the Bootleg carrier and Select Adjustable Gas Block look to be very solid designs, and great options for those looking to add an adjustable gas feature to their rifles. After all it’s 2020, so why stick with a gas system designed in the 1960’s? Sure, the phrase “if it aint broke don’t fix it” does have merit, but don’t let it hold you back from improving the performance or your AR.

Bootleg Four Position Carrier
bootleginc.com

Seekins Precision Select Adjustable Gas Block
seekinsprecision.com

Barnes Precision Machine Accu-Set Adjustable Gas Tube
usamade-ar15parts.com

About the Author:
Jeff Gurwitch is retired U.S Army Special Forces (SF).
26 years active duty, 19 years with SF.
15 years’ competitive shooting experience; USPSA, IDPA and 3 Gun.

© Copyright 2020 DefenseReview.com (DR) and Jeff Gurwitch. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without receiving permission and providing proper credit and appropriate links.

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Tame that Gas! Improving the Direct Gas Impingement (DGI) Tactical AR-15 Rifle/Carbine at Relatively Low Cost by

About David Crane

David Crane started publishing online in 2001. Since that time, governments, military organizations, Special Operators (i.e. professional trigger pullers), agencies, and civilian tactical shooters the world over have come to depend on Defense Review as the authoritative source of news and information on "the latest and greatest" in the field of military defense and tactical technology and hardware, including tactical firearms, ammunition, equipment, gear, and training.

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