Firearms

Adjustable AR Gas Blocks

AR-15 bolt carriers

This last weekend, I provided a buddy a side-by-side comparison of his standard AR and one of my AR-15s with an adjustable gas block. His actual quote was, “Holy crap! When can you do that to mine?” Your first experience with an adjustable gas block will be an enlightening one. The near absence of recoil and almost non-moving sight picture is stunning to say the least, in the “Holy crap! Why did I not do this before?” kind of way. I maintain that an adjustable gas block is the most significant performance upgrade anyone can make to their AR-format rifle.

By Major Pandemic

Hex wrench adjusting the gas block
Need to hide an adjustment screw just in case? Hide one in the handgaurd barrel nut holes with high heat tubing and a hex wrench.

After my very first JP adjustable gas block, I was sold on the having the ability to tune the gas pressure on a standard direct impingement AR-15 system. The advantages are a plenty with a large reduction in recoil, faster recoil recovery, faster sight picture acquisition between shots, heat reduction at the bolt, and a bit cleaner running, all being the primary advantages.

A History & Why We Need Adjustable Gas Blocks on AR-15 Rifles

All things in the gas system must be in a Zen state of balance, and generally on an AR-15 direct impingement system, they are pretty unbalanced—tipping gluttonously in favor of a guarantee of reliability while making the deep sacrifice of heavier recoil in the process.

A direct impingement system works pretty simply: the round fires, the bullet travels down the barrel, the pressure is leached off via a gas port (small hole) in the barrel which pushes gas up into a gas block, the gas block reroutes the gas back down the gas tube and back into the BCG (bolt carrier group), that pressure presses on the bolt O-rings inside the carrier which unlocks the bolt and cycles the action. Repeat until the magazine is empty. The length and internal dimensions of gas tube, size of gas port in the barrel, internal dimensions of the gas block, placement of the gas block on the barrel gas port (correctly or incorrectly), barrel length, type of compensator or suppressor, placement of the gas port on the barrel more forward or backward, friction of the BCG, position and condition of the O-rings on the bolt, weight of the buffer, rate of the buffer spring, weight of the rifle, rate of powder burn of the ammo, amount of powder, how hot the primer is, bullet weight, whether the BCG bounced during the last cycle and is oh-so-slightly out of battery or not, a shooter’s shooting style, and more all play roles which much be kept in a Zen-like balance for functioning to work at the rifle’s optimum tuning point. Generally though manufacturers have erred on the obscenely over-gassed side to guarantee reliability… even if it does beat up the shooter and components.

AR-15 bolt carriers
Adjustable gas blocks can help optimize any light or standard weight bolt carrier group.

For many of us, the palm to the forehead/illuminating moment comes when we try a mid-length, or rifle-length, gas system with less recoil, and that seemed to run longer, cleaner, and cooler to some degree—all while being more reliable. Hmmm, less gas pressure.

All an adjustable gas block does is adjust gas pressure just like a faucet does with water. Even by turning that gas pressure down significantly, most gas system are so over-gassed that total reliability can still be had all while delivering huge benefits to the shooter. Today, we can control gas pressure with adjustable gas blocks like those from Superlative Arms. By using lighter weight Bolt Carrier Groups from Young or JP and low mass buffers and springs, we can turn the gas down even more for an amazingly light-recoiling AR-15.

How Adjustable AR Gas Blocks Works

Most people view the adjustable gas block in the same mindset as a fad like Shake Weights or Chia Pets instead of the innovation that it is. Oddly, many of these doubters I have talked with seem to embrace the adjustable piston systems which [cough] are in essence adjustable gas systems [cough], but they think adjustable direct impingement systems somehow have less merit. I am a believer in adjustable gas systems, I have shocked and awed myself and others during testing with the dramatic metamorphosis which occurs from transforming a punchy 5.56 AR-15 to a flat, soft, and fast shooting firearm by just by reducing gas pressure.

the JP Adjustable Gas block installed on the upper.
The JP Adjustable Gas block installed on the upper.

Generally, all “adjustable” gas blocks work the same. A screw simply pinches closed the gap between the barrel gas port, and the gas tube just like a faucet controlling a stream of water.

There is now a ton of adjustable gas blocks on the market that offer a screw stuck in a gas block. The idea is so simple even a lightly skilled individual such as me has converted many standard gas blocks to adjustable versions. The most significant problem becomes locking in the adjustment. This is where the patented Superative Arms and SLR adjustable gas blocks are a best option. It locks into position with a detent so the adjustment will never move on you.

How To Tune An Adjustable Gas Block For Performance & Reliability

  1. Assure the firearm is unloaded and the chamber is clear. (Syrac recommends tuning on a dry un-oiled-rifle with the lightest load you will use.)
  2. Carefully, turn the adjustment screw all the way down clockwise until it bottoms out, approximately three full turns and then back off one full turn.
  3. Load one round in the magazine and seat the magazine.
  4. Shoot the gun with an offhand shooting position. Bolt should lock back
  5. If BCG locks back, complete 6, if not complete 7.
  6. If the BCG locks back, turn the screw clockwise in ¼-turn increments repeating the steps 4-5 until the bolt no longer holds back, then back out counter-clockwise ¼-turn and proceed to step 8.
  7. If the BCG does not lock back turn the screw counter-clockwise in ¼-turn increments repeating the steps 4-5 until the bolt holds back and proceed to step 7.
  8. Increase in counter-clockwise ¼-turn increments as needed until the bolt holds back successfully three consecutive single-round shots.
  9. If successful, your AR-15 is now optimally tuned for that ammo.
  10. If concerned with assuring reliability with a broader range of ammo, then add ¼- or 1/2-counter-clockwise turn. You will get a bit more recoil, however your reliability will increase if you swap ammo a lot. I usually add 1/2-turn and rarely have any problems going forward with any ammo.
    Note: If you move an upper to a different lower assure you use the buffer and buffer spring from the lower used to tune the upper, otherwise the gas block should be re-tuned.

Tuning Observations

Once you get things set up and tuned plus that 1/4 or 1/2 extra counter-clockwise turn, you will rarely if ever have any reliability issues all while enjoying a better shooting AR.

DIY Adjustable gas block
This DIY Adjustable gas block works just as well as the commercial versions.

With an adjustable gas block, a standard AR-15 BCG, buffer and buffer spring is actually preferred instead of heavier H1, H2 variants and will allow a lower gas pressure setting and net you the biggest benefit of recoil reduction. After all, a lighter BCG, buffer and buffer spring requires less gas pressure to move.

If you move an upper to a different lower assure you use the buffer and buffer spring from the lower used to tune the upper, otherwise the gas block should be re-tuned. Additionally changes to muzzle brakes or flash hiders, changes to buffer, buffer spring, carrier, bolt, and handloads or low velocity rounds may require re-tuning for optimal reliability.

Final Thoughts

Adjustable gas blocks deliver a dramatic advantage for AR owners and, in my opinion, are the most significant performance upgrades you can make to shoot faster, reduce fatigue on you and your firearm, and potentially make your AR-15 shoot longer without the need for cleaning. Adjust away!

Gas maskMajor Pandemic is an editor at large who loves everything about shooting, hunting, the outdoors, and all those lifesaving little survival related products. His goal is simple, tell a good story in the form of a truthful review all while having fun. He contributes content to a wide variety of print and digital magazines and newsletters for companies and manufacturers throughout the industry with content exposure to over 2M readers monthly. www.MajorPandemic.com

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (8)

  1. Ya that all good until you have to shoot a different ammo then Ajustible gas block my get you killed in real War / life moment !

  2. I am 1/2 way through my first build, which was originally intended to be chambered in 7.62 x 39. I have a heavy buffer tube for it. Now, to help on costs I’m thinking of changing the caliber to 5.56. Will the heavy buffer tube assembly be an issue with the lighter 5.56 & adjustable gas block?

    1. I put a Syracuse Ordnance detent adjustable gas block gen 2 on my AR build. It’s low profile so it goes under my ATI free floating hand guard. With the detent you don’t have a set screw to lock the adjustment screw so therefore there’s no need to take it out to put lock tight back on it every time you adjust it or take off the hand guard or put a hole where the set screw that locks the adjusting screw. You can fine tune the gasses to reduce recoil and it runs cleaner with a nickle boron BCG all I have to do is wipe it clean with a alcohol wipe, no scrubbing it because I don’t get carbon build up. A spikes ST-T2 heaver buffer goes hand in hand with the gas block when you shoot your spent shells should land at 3 o’clock. Anything from 12 to 2 is overgased and 3 to 6 is undergased. I would never build a AR without a adjustable gas block, free floating hand guard or a spikes ST-T2 heavy buffer.

  3. Do you have any experience with an adjustable block on a 9mm or 40 cal upper? Same procedure?
    What about if you are lucky enough to live in a state that allows you to shoot with a can? Any advice for those accessories?

    1. Pistol caliber AR’s do not have gas systems as their BCG are non-locking. Instead they work off of direct blow back with heavier BCG, buffers and springs to delay the action cycling until chamber pressures have lowered.

      Most suppressors increase the amount of gas into a DI system. It is nice to be able to reduce the gas needed to operate the action while running a suppressor. Their are some suppressors that have less “blow back” effect keeping the system less over gassed, however, they tend to not be the quietest cans available.

  4. I tried the adjustable gas block routine and found it to be a big pain in the butt. Never could find the sweet spot unless I bought the wife a box chocolate. My findings, when enough carbon built up in the gas block it was impossible to depress the blocks button in order to adjust the set screw. Only a complete disassembly of the hand guard exposing the block made it possible to correct the situation. I eventually went back to old school gas block remembering what someone told me many years ago.” If it ain’t broke don’t fix it.

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