An Adjustable Gas Block – why, what, and how.

First of all, we need to understand how a gas gun (the AR) works.

Essentially, a gas gun uses some of the gas that is propelling the projectile to also cycle the gun. In an AR, this gas is fed back to a cavity between the bolt and the carrier via the gas block on the barrel. The gas pushes the carrier rearward which in turn unlocks the bolt. The carrier continues rearward under its own inertia, pulling the bolt along with it and extracting the spent casing. The bolt carrier group travels to the rear of the buffer tube resetting the hammer in the process and allowing the spent casing to be ejected. The action spring in the buffer tube then pushes the bolt carrier group forward, picking up another round and chambering it. Putting the gun into battery – ready to fire again.1

With a factory, unmodified rifle – it is quite possible that a lot more gas than is required to operate is pushed back into the chamber. While this ensures good reliability and the ability to cycle any ammunition you are likely to feed the rifle, it also means you may be experiencing more recoil, more wear and more gas spitback (ask a leftie shooting a right ejecting AR about this) than is necessary.

Suppressing a Gas Gun

Now, put a device on the end of your barrel that essentially ‘holds back’ even more gas and you can see we have now created a situation of ‘over-gassing’ – that is, driving way more gas back into the chamber than required. We are now at the point where we might be driving the gun harder than the factory intended, so it becomes a very good idea to find a way to reduce the amount of gas that is going back down into the chamber and bolt.

Reduce the gas, reduce the recoil

The gas that is sent back towards the shooter affects how fast and hard the bolt slams back in the receiver – this is felt by the shooter as part of the recoil pulse. First, we feel the recoil of the gases coming out of the barrel, secondly, we feel the recoil and the bolt physically moves back in the receiver and cycles the gun. By reducing the amount of gas that is sent back into the chamber, we can reduce how hard the bolt (and buffer) has to work. This can result in a lighter firing gun – meaning, less perceived recoil, quicker follow up shots and a smoother gun to shoot.

However, to little gas, and the bolt won’t be able to reset properly. This could result in the bolt not going back far enough to pick up another round.

Muzzle devices on the end of the barrel will affect how much gas gets sent back (a suppressor increasing it a lot) and the type of ammo and how much pressure it generates will also change the operation of the gas system.

Tuning the Gas System

If we are able to essentially tune the amount of gas being sent back, we can find a sweet spot on the rifle where the ammo used generates enough pressure to reset the firearm reliably, but reduces the additional kickback and therefore keeps recoil down.

Because we are likely to want to take the suppressor on and off, and, because people like to try different ammo for different purposes, a gas block that allows to you selectively change the amount of gas being sent back to the chamber become a very good idea. Hence, the adjustable gas block.

08:02

The AGB2 from D.F. Maisey Gunsmithing

Dean Maisey is a name well known for quality gunsmithing work. Based in Tauranga, the only complaint I have ever heard about him is simply the fact that he is always so busy, there is a bit of a waiting time to get work done. This is a result of plenty of people wanting the services on only one man.

In addition, though, Dean also manages to find a bit of time to develop his own muzzle breaks, suppressors and, the subject of this article – adjustable gas blocks.

The AGB2 is the second generation of Dean’s adjustable gas blocks. The AGB1 is still available, but it is the slimline AGB2, designed to fit under the modern free floating handguards that are often seen in competition these days, that may be of more interest to you guys.

The main feature, for me, that makes everything so much easier – is the detented (i.e. clickable) adjustment screw. This means once you tuned the system (see the video for details on how to) – you simply remember the amount of clicks from closed for that particular ammo/muzzle device combo, and can quickly adjust from one setup to another. It is so easy. In addition, there is no ‘lock-tite’ to apply, and no chance that the setup will change on you.


  1. thanks to Alex McKenzie for the awesome rework of this section! 

Rifle Setup Service

$ 750 /day
Spend a day learning how to properly setup your rifle, including stock adjustments, scope mounting, eye relief and more.

Despite what they may say, many stores do the absolute minimum when it comes to setting up your new firearm. Learn how to get the most out of your investment.
  • Properly Zero'd
  • Setup for you
  • Basic ballistics
  • Ready to go

Popular articles

Whoa whoa whoa… where did Precision Shooter go?

While it would be easy to say that rebrand was a result of the tragic events in recent history, it was actually...

Changes in the Semi-Automatic Classification System

I have been quiet since Friday, and for good reason, but let's try and clear up some of the confusion about today's firearms law announcement.

The Swarovski dS – Scope, rangefinder, ballistic solver.

It's the pinnacle (price wise at least) of 'smart' optics. But does the price of the Swarovski dS really equate to value? Like many things premium, it's a yes, no, yes, kinda answer.

Matching twist rate and bullet weight in rifles.

The are many benefits to understanding and matching the twist rate of your barrel with the projectile weight you are using. Primarily, accuracy.

The Stage 1 is for sale. Again.

So, I finally blew it up. The engine in the Stage 1 now has a fairly large hole in it.

Stop the Bleed. Prac Med’s IFAS Kit first look

So, should you, are someone near you have a major issue with losing a LOT of blood, do you have the resources on you to stop it?
Kerry Adams
Kerry Adamshttps://thebloke.co.nz
A constant learner with an inquisitive mind, Kerry created Precision Shooter as a way to share what he was learning from the community of experts he found himself surrounded by.Somewhere along the line, he picked up one or two things himself. But don't call him an expert.
I know. We all hate popups.
But, the fact remains that eMails are the best way for us to keep you up to date with what is going on at The Bloke.Join over 17650 others who are part of The Bloke community - every week you will get a short update from me. Be the first to know about new resources, upcoming events, courses and more.
We respect your privacy. No SPAM. Ever. Hit escape to make this go away. Apologises if you see this more than once. That's what cookies are for... ;)