- Ejection pattern or lack of ejection can be used to determine proper gassing
- Over gassed ARs have greater parts wear and more felt recoil
- Under gassed ARs have weak or no ejection
Have you ever wondered how to tell if an AR is over gassed or under gassed? Knowing if your rifle is running properly is the best way to make sure you avoid unnecessary issues. How well a rifle is gassed is a big determining factor for how long a rifle will run without breaking.
We’ll cover how to determine whether your rifle is over gassed or under gassed, in addition to what you can do to fix the issue.
How To Diagnose An Over Gassed AR
Diagnosing an over gassed AR-15 is relatively easy. If the rifle is ejecting at the 1 or 2 o’clock position, it is over gassed. This is because too much gas is being vented back into the system, causing the bolt to cycle faster than the case can be ejected from the chamber.
Another way to diagnose if your AR-15 is over gassed is the felt recoil. If your AR-15 is violently recoiling, you are over gassed. This is easier to determine if you have shot multiple AR-15s to have a reference for a proper amount of felt recoil.
Over Gassing Issues
Does it matter that your rifle is over gassed? Yes. While having an over gassed rifle can allow it to keep running through a lack of maintenance and the dirt and grime of the outside, it will take a toll on your rifle’s parts.
Damaged extractors, damaged bolts, accelerated wear on springs, and more can be caused by over gassing your AR-15. This is on top of the unpleasant experience of shooting a gun that is slowly beating itself apart.
Keeping your rifle properly gassed will increase its lifespan and provide a better shooting experience.
| Pros | Slightly better performance in adverse conditions |
| Cons |
Greater felt recoil Greater parts wear Higher chance of catastrophic malfunctions |
Fixing an Over Gassed AR
This brings us to how to fix an over gassed AR-15. There are a few ways to handle this. The easiest way is to use an adjustable gas block and adjust the settings. But not everyone has an adjustable gas block, and some rifles just have too much gas in them for your preferred ammunition.
If changing the gas block doesn’t work or is not an option, the answer lies in your buffer tube. Changing the buffer or using a heavier buffer spring can help with mitigating an over gassed rifle. This is because it will take more effort to cycle the bolt, eating up that rearward energy.
Too much gas in the system means there will be excess energy with nowhere to go. So finding ways to either limit energy consumption or use it efficiently will be your solution.
How To Diagnose an Under Gassed AR
At the opposite end of the spectrum, there is the situation where insufficient energy is entering the system. An under gassed AR-15 will eject a case weakly or not at all. The brass cases will almost fall out of the gun or the bolt will barely move.
Additionally the bolt may not fully cycle. This means it won’t go far enough back for the ejectors to engage, leading to a number of classic malfunctions.
Under Gassing Issues
Under gassed AR-15s are more prone to malfunctioning. This means issues such as stovepipe malfunctions and doublefeeds. This is because not enough energy is being exerted on the case to throw it out of the gun as Eugen Stoner intended.
This increases the likelihood of multiple failures occurring simultaneously. However, extreme cases of undergassing will exhibit the gun not cycling at all. This will be evident when the bolt barely returns after the gun is fired.
If the gun doesn’t cycle, it is unreliable and needs to be fixed as soon as possible.
| Pros | Potentially fixed with suppressor use |
| Cons |
Weak or no ejection Potential double feeds |
Fixing an Under Gassed AR
Now how to fix an under gassed AR-15 is a little more in-depth than fixing an over gassed one. You will need to check the gas block to see if it is properly fitted. If it is not, it will leak gas throughout the process.
If the gas block is on correctly, check the gas tube and gas key next. If the tube is not fully seated or the gas key is not properly staked, you will lose gas at these locations. Additionally, the gas rings may be worn and require replacement.
Closing Thoughts
Reliable performance should be the goal of every AR-15, and knowing how to tell if an AR is over gassed or under gassed goes a long way in figuring that out.
If you have a rifle you want to be a dedicated suppressor host and it uses a suppressor that increases back pressure, a slightly undergassed rifle is going to be beneficial. The reason for this is that the extra back pressure brings the under gassed rifle back into the appropriate pressure ranges for the rifle to function.
If you have a rifle that will be doing it all, it needs to be properly gassed or biased moderately towards over gassed. Too much in either direction will cause issues, it’s better to run everything to the rifle’s specifications and tune it to your needs later.
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