Monday, February 28, 2022

All About Adjustable AR Gas Blocks

All About Adjustable AR Gas Blocks

This last weekend, I was at the range with a buddy who was hammering through rounds on his custom 18” Mid-length AR.  It is a great rifle which shoots very well but does not have an adjustable gas block. Then I pulled out a couple ARs with JP, Syrac Ordnance, and even some home brewed adjustable gas blocks for him to feel the difference.  His actual quote was “holy crap, when can you do that to mine”.  I will almost guarantee that 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 have actually had people flip the AR to the left to check if they were firing an .22LR conversion, but rest assured, it is not magic, it is not voodoo, it is though, just simple physics.

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 AR15 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. 

All things in the gas system must be in a zen state of balance, and generally on an AR15 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.  
My DIY Adjustable Gas Block on my Model 1 Sales
Dissipator Build - Hidden under a Troy Extreme Rail
A direct impingement system works pretty simply; round fires, bullet travels down the barrel, 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.  

Through that process, you can see that there are a fair amount of timing dependant items which need to work in concert for everything to function, but lucky for us Mr. Stoner was a genius who built a system which could tolerate a pretty significant amount of slop and manufacturing error and still work.  

Installed -My DIY Adjustable Gas Block on my Model 1 Sales
Dissipator Build - Hidden under a Troy Extreme Rail
But, ah ha, there is more to the story.  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.  
Check out the Superlight YM AR15 Carrier.  
Bolts Shown - Del-Ton AR15, Spikes M16, 
Fail Zero M16, YM Superlight, YM M16 National Match, 
Model 1 AR15 with JP Bolt, DPMS AR15 
with Model 1 Chrome Bolt
It would be difficult and irritating to have a firearms which were tuned for an optimum point and then not work right when something as simple as a shooter’s grip could throw off the functioning. The reality is we can tune an AR to perform closer to an optimal state however, we will always have to error on the reliability side with a little extra recoil and gas pressure to assure functioning.  

Today we can control gas pressure with Adjustable Gas Blocks like those from Syrac Ordnance, use light weight BCG from Young or JP and low mass buffers and springs, however as we approach closer and closer to the optimum gas system tuning point the more picky the firearms will become to ammo changes. This is because bullet weight and cartridge velocity begin to proportionally become more and more important to functioning. I have heard of some heavily tuned race focused 3-gun ARs which will only function with rounds within a narrow velocity and bullet weight range, but for those guys they have the option to only use that one ammo if they like.

Generally though, AR15’s are setup for reliability and just blow a shitload of gas back into the action to totally overcompensate for a general lack of engineering or understanding of the other variables. This is kind of like saying you need to kick closed every car door regardless of the car, because you had a Ford Van in 1972 that had a door that needed to be kicked closed.

Syrac Ordnance Clamp on Adjustable Gas Block 
& Set Screw version in forground

With the understanding that all direct impingement even mid and rifle-length systems are over-gassed by a little, or a lot, we have attempted to reduce recoil and run time failures by optimizing the tuning of the gas system.  Unfortunately we have done this not by addressing the main problem of too much gas, but by adding heavier upgraded components typically used to tame full auto cycle rates on short barreled military spec M4 rifles.  

Because we have too much unregulated gas, we can either decrease the gas pressure or increase the mass/weight of the components being affected by gas pressure to balance things out. This has lead to people using marginally heavier M16 carriers, heavier buffer springs, then heavier buffers, even heavier, and wow-really that heavy of a buffer. In most cases, the weight seemed to do the trick, however in my opinion we fixed the issue incorrectly and added weight and stress to the entire system. After all, if a little puff of air to a light bolt, buffer and buffer spring will do the job all while delivering less fatigue to the components, then why would we complicate things? Well for one, the general populace can venture too close to the tuning window edge and begin complaining that their rifle being unreliable... and in fact we have seen that with a few tunable piston systems which require hotter rounds to function. 
The JP Rifle Adjustable gas block is
among one of the most well known.

For many of us, the palm to the forehead/illuminating moment came when we started going back to mid-length and rifle-length gas systems which have less gas pressure than our carbine versions, less recoil, seemed to run longer, cleaner, and cooler to some degree, all while being more reliable. Hmmm, less gas pressure.

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 AR15 to a flat, soft, and fast shooting firearm by just by reducing gas pressure.

Because adjustable gas blocks also allow you to adjust the gas pressure, a carbine can have the same shooting feel as a mid-length, rifle-length gas systems or obviously even far less recoil than either of those gas systems. No longer do the carbine length rifle get shortchanged. I you you really want to toy around with reducing recoil, JP makes light weight Low Mass buffers and JP & YM both make low mass light weight carriers as well which will let you dial down gas pressures even further.
Look closely just in front of the picatinny rail and
you can see the adjustable gas block's grub screw I DIY'ed
on this Spikes Tactical ST-15 Front Sight Gas Block
With some exceptions, 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.  Micro-MOA is the only company which uses a sliding plate assembly.

There are now a ton of adjustable gas blocks on the market which offer a screw stuck in a gas block. The idea is so simple even a lightly skilled individual such as myself has converted three standard gas blocks to adjustable versions on a two carbines and one mid-length rifle system. THE most significant problem becomes locking in the adjustment.  On some of my home brew versions, unless I have been studious about permanently lock-tite-ing the screw in place, I begin to see pressures slowly increase as the screw starts to walk out.  This is where the patented Syrac Ordnance or SLR Rifleworks adjustable gas blocks are the best options.. it locks into position with a detent so the adjustment will never move on you.


  1. Assure the firearm is unloaded and the chamber is clear
  2. Syrac recommends tuning on a dry un-oiled rifle with the lightest load you will use.
  3. 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.
  4. Load one round in the magazine and seat the magazine
  5. Shoot the gun with an offhand shooting position. Bolt should lock back.
  6. If BCG locks back, complete 6A, if not complete 6B.
6A. 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 7.
6B. 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.
  1. Increase in counter-clockwise ¼ turn increments as needed until the bolt holds back successfully three consecutive single round shots.
  2. If successful, your AR15 is now optimally tuned for that ammo.
  3. 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.
  4. 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.
  5. NOTE - Changes to muzzle brakes or flash hiders may require re-tuning.

SLR Rifleworks Adjsutable Gas Block with Detent
Currently My Favorite Gas Block Made

At this point I have converted nearly a dozen AR15s with adjustable gas blocks in pistol, carbine, mid-length, and rifle-length systems of which I have made many adjustable gas blocks with just a carbide drill bit and threaded worm screw. I have learned a thing or two in the process, but I am am still learning each and every time I start swapping this or that around and change variable the gun operates under. Once you get things set up and tuned plus that 1/2 extra counter-clockwise turn, you will rarely if ever have any reliability issues all while enjoying a better shooting AR.

With an adjustable gas block, a standard AR15 BCG, buffer and buffer spring is actually preferred instead of heavier variants and will allow a lower gas pressure setting and net you the biggest benefit of recoil reduction. 
I have even lightened a rifle length buffers since they are heavier than carbine buffers. After all, a lighter BCG, buffer and buffer spring requires less gas pressure to move.
Store a hex key conveniently for adjustments

It has been my experience that heavy buffers, heavy buffer springs, and M16 carrier groups increase tuning complexity as this extra mass is more sensitive to gas pressure and ammunition changes. ARs with these heavier components will require a higher gas pressure setting for operation, and will deliver slightly more recoil when compared to systems with standard components, but that does not mean that you should run a wooden buffer either.

If installed on a defensive rifle I would add at least a ½ to 1 full turn to assure reliability and test three round functioning drills with a couple boxes of different bullet weights to assure total functional reliability with your chosen defensive round.
DPMS Oracle DIY Adjustable Gas Block
Peeks through a PRI Forend Some forend
modification may be required for side 
adjustable gas blocks
Personally, I have found that ½ turn extra seems to provide a broad envelope of reliability for a variety of rounds unless you tend to shoot less expensive Tula and Herter’s ammo which are on the bottom of the .223 SAAMI spec range.
Contrary to rumors on some forums, so far, none of my adjustable gas blocks have required special cleaning or cleaning of any kind.

One little trick is to attach the appropriate hex wrench with a little high heat silicon tubing (from most hobby stores) through a hole in the forend nut. It is always there handy in case you need to do a re-tune.

The most optimal tuning state would be swapping out to the lightest BCG, buffer, buffer spring, and gas setting possible while still assuring reliability.  I am planning a future article just on this subject using the Syrac Ordnance gas block and a set of Young Manufacturing YM Super Light AR15 and heavy National Match M16 bolts for testing.
Syrac Ordnance Adjustable Gas Block
Adjustable gas blocks with forward facing adjustment such as Syrac's are much easier to adjust than typical side mounted adjustment, especially when extended forends are utilized. 

With the exception of the Syrac Ordnance detented gas block, permanent Lock-Tite is a requirement for any gas block, home brewed or otherwise.  

Keep a log book of which ammo you have tested in the gun and what adjustments you have made.  This should give you a good high low range of adjustment to work with in the future.

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.

Although, my garage created adjustable gas block concoctions work perfectly, I would recommend JP, SLR or Syrac Ordnance Gas blocks. The JP models offer a top picatinny rail and Syrac Ordnance provide a low profile alternative which slip under even the skinniest handguards.  From my understanding Syrac will be licensing their gas block patent to several manufacturers. SLR has a bit different design which features a detent for each setting to assure that the set screw will not slip out of adjustment.

Adjustable gas blocks deliver a dramatic advantage for AR owners and can be one of the best upgrades you can made to shoot faster, reduce fatigue on you and your firearm, and may potentially make you AR15 shoot longer without the need for cleaning. 
The sizable recoil reduction can made a huge difference to those who are a little sensitive to recoil and I usually start off new shooter with the very light DMPS Oracle build (shown below) with a Phase 5 muzzle brake and New Frontier polymer lower with a home brew adjustable gas block. The build is joking referred to by all as the squirt gun because of how light it shoots after the conversion. 

AKA - The Squirt Gun
Sure adjustable gas block do require a little tuning and if you swap a low end lower pressure ammo you may have to do a bit of re-tuning to get the reliability you want, however the effort is completely worth it. Adjustable gas blocks make a huge difference in shooting comfort and swapping out gas blocks is a fairly simple task especially if your existing gas block is not pinned. This is an upgrade I strongly encourage.


Shop the complete selection of Adjustable Gas Blocks at 

JP Rifles

Syrac Ordnance

SLR Rifleworks

Read the review of the Syrac Ordnance Gas Block