America’s Rifle is a fine-tuned machine, and you know what happens when that tuning falls short or goes out of whack: things don’t work as they should.
Case in point, an AR gas system should siphon off just enough gas under just the right pressure to engage the bolt carrier group’s gas rings, unlock and throw the bolt to the rear so that the buffer system can complete cycling.
Now, to be fair, it’s not just about the AR gas system. The buffer weight and spring must also be tuned to the gas system, as well as to the caliber in general and the weight of the bullet in specific.
But when the rifle is overgassed (or undergassed, for that matter) you’ll start to see some hiccups. Here are some things to pay attention to and what you can do about it.
How to Tell If Your Rifle Is Overgassed
There are some big symptoms that can tip you off that your gun is overgassed. The big one is extra recoil, especially if you’re familiar with the ammo you’re shooting. Often a little extra punch to the shoulder, more than you’d expect with the caliber, is the big sign.
When you strip your gun and drop out the bolt carrier group after a day at the range, if you notice it’s completely covered in fouling, that’s another sign that there’s just too much pressure in the bore, which is another big sign of overgassing. Prematurely worn gas rings can also indicate overgassing.
Ejection patterns can also tell you about whether or not your AR’s gas system is properly tuned. An overgassed rifle tends to spit out casings too far forward. Because an overgassed rifle will throw the bolt carrier group backwards with too much force, the shells will usually eject between the 1 and 3 o’clock positions.
If your rifle is suppressed and you’re getting too much gas in your face when the action cycles, that’s another sign that your AR gas system might be running a little hot.
Overgassing can be a concern with AR15 pistol uppers that use a gas system instead of direct blowback because these tend to shoot hot as it is. You don’t want an ARP upper seriously overgassed or its bolt will wear out prematurely.
What to Do
Now that you know what to look for to tell whether or not your rifle is overgassed, here are a few steps you can take to remediate this issue.
First, if your rifle has a fixed gas block, and many do, the step to take here is to replace the fixed gas block with an adjustable one.
Once you’ve replaced the gas block, when you’re at the range, fire three to five rounds as a group, restricting the gas each time until the issue resolves itself.
How to Tell If a Rifle Is Undergassed
While overgassed rifles present a potential issue, so too do undergassed rifles, in which less than desired gas is delivered to the bolt carrier group’s gas rings.
If a rifle is undergassed, one of the main signs will be “short stroking.” Short stroking occurs when the bolt carrier group does not fully cycle. This can result in jams, partial extraction/ejection, and failure to chamber a fresh round.
However, some undergassed guns may still cycle, but will eject the shells too far to the rear, between the 4:30 to 6 o’clock positions. While jams may not occur, it’s important to tune the AR gas system so that more pressure is used to cycle the BCG, as it’s more or less a matter of time until the insufficient gas pressure results in jams or failures to feed.
What to Do
Most rifles are a little bit overgassed from the factory, which makes overgassing a relatively easier problem to solve. If your rifle has an adjustable gas block, you can simply open up the gas port a little to let more gas through to the bolt carrier group.
If, however, your rifle is still undergassed and it either has a fixed gas block or an adjustable gas block that is tuned so that it is open all the way, you may need a trip to the gun smith to open up your gas port all the way.
Before you do that, though, you will want to make sure that you know your problem is undergassing. Some of the problems associated with undergassing here could also be caused by inadequate buffer weights or a buffer spring that is starting to fatigue.
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Being able to diagnose over or undergassing in your rifle or AR15 pistol is critical to tuning performance. Whether you are here for gas system parts, an AR upper, or an AR15 pistol upper, we have what you need, including assembled uppers. Check out our full catalog and if you have any questions, get in touch with us at Sales@MCSGearup.com.