What is a AR15 Gas Block


All Out Info About Adjustable AR15 Gas Blocks

I hang out at the range with a friend who was shooting rounds with his 18” custom Mid-length AR.  It’s a pretty nice rifle that which shoots very well; only, I noticed that it doesn’t have an adjustable-type gas block. What I did was pull out some ARs with JP Syrac Ordnance, then a few home-crafted adjustable gas blocks for the guy to hopefully feel the difference. My  buddy’s actual reply was “Holy crap, how? Why didn’t I think of doing this before with mine?”

I’m almost one hundred percent sure that your first ever experience with an adjustable gas block, too, will feel an enlightening one. To say the least, its almost non-moving picture sight and near-absent recoil and is awesome. I’ve actually made some people flip their ARs to the left side to see if they were in fact firing an .22LR conversion. I rest assure, this is not at all magic or voodoo. It’s purely physics.

So after my first encounters with JP adjustable gas blocks, I was next sold on being able to tune gas pressure on an AR15 system standard direct impingement. It has plenty of advantages including large reduction in recoil, faster in-between shot sight picture acquisition, faster recoil recovery, cleaner running, and heat reduction down at the bolt.

Background:  Reason Why We Need an Adjustable Gas Block on an AR15 Rifle

On a direct impingement AR15 system, generally, things are rather unbalanced siding heftily in favor of having guaranteed reliability while deeply sacrificing heavier recoil. And everything in the gas system should be in a state of Zen balance.

It’s pretty simple how a direct impingement system actually works: round the fires, bullet traveling down the barrel, pressure leaching off via a small hole (gas port) in the barrel that pushes the gas up into the gas block, gas block rerouting the gas back down into the gas tube then back into the bolt carrier group (BCG), pressure pressing on the bolt o-rings found inside the carrier, the bolt unlocking and everything cycling the action. This process is repeated until the magazine is completely empty.

In the process, you’ll probably notice several timing dependent components that need to work together in perfect for everything to function correctly; but great thing for us all, Mr. Stoner, a true genius, built a system that could effectively tolerate a good significant amount of spills and manufacturing errors for everything to work perfectly. But still, alas! There’s more behind this story.

More things play significant roles in the proper functioning of an AR15 which all much be kept in perfect Zen-like balance to contribute to the rifle’s optimal tuning point:

  • barrel’s length
  • gas tube’s internal dimensions, length, etc.
  • gas block’s internal dimensions,
  • barrel gas port’s size,
  • correct or incorrect gas block’s placement on the barrel gas port,
  • more forward or more backward gas port’s placement on the barrel,
  • bolt o-rings’ position and condition,
  • type of suppressor or compensator,
  • rifle’s weight,
  • buffer’s weight,
  • buffer spring’s rate,
  • bullet’s weight,
  • BCG’s friction,
  • ammo powder burn’s rate,
  • amount of powder,
  • hotness of the primer,
  • whether or not the BCG bounced is the last cycle or if it is ever-so-slightly out of battery or if not,
  • the shooter’s particular shooting style, etc.

It would be troublesome and annoying if your firearm is tuned for optimal point, however would not work right all because something as simple as the grip of the shooter is throwing off the rifle’s entire functioning. But the real deal here is that we can help tune an AR15 to perform much closer to its true optimal state. The only condition is that we will always need to err on the reliability side, adding a little extra recoil as well as gas pressure in order to assure optimal functioning.

On the other hand, approaching closer and closer to the tuning point of the optimum gas system, the more picky to ammo changes the firearm will also become. The reason is because cartridge velocity and bullet weight begin to be more and more proportionally important to functioning. I’ve encountered some heavily tuned race focusing 3-gun ARs that will only work with rounds within narrow range bullet weight and velocity, but for these there is the option of use only that one ammo if it’s the preference.

In general though, AR15’s are geared for better reliability while blowing a shitload of gas right back into the action in order to overcompensate totally for the system’s general lack of engineering for the other variables. It’s some kind of like saying that you need to kick every car door closed regardless of the car type, because you once had a Ford Van in 1972, the door of which needed to always be kicked closed.

With some understanding that each and every direct impingement system even mid and rifle-length ones are a little over-gassed, or a lot over-gassed, by optimizing the gas system’s tuning, we have tried to simply reduce recoil as well as run time failures.  Sad to say, this is not addressing the main issue of having too much gas, but simply by adding heavier upgraded parts used typically to help tame full on auto-cycle rates on military spec M4 rifles that are short barreled.

And since we have too much gas, all we can do is either 1) decrease the gas pressure or 2) increase the weight/mass of the parts that are affected by the gas pressure just to balance everything out. Thus, people use marginally heavier M16 type carriers, heavier buffers, and heavier buffer springs.

In a lot of cases, this weight adjustment seems to do the trick, but still, since we didn’t fix the issue correctly, we just added weight to add stress to the whole system. The general populace, for one, can try getting too close to the edge of the tuning window and then start complaining that their trusty rifle is now being unreliable… As a matter fact, in some tunable piston systems requiring hotter rounds just in order to function, this is pretty much the case.

For many of us, an especially enlightening moment came when we reverted back to using mid- and rifle-length gas systems that have lesser gas pressure compared to our carbine versions, plus less recoil. It seemed to run cleaner, cooler longer, and to at some rate, totally being more reliable so… less gas pressure it is.

Why should we complicate things further if just a little addition of air to the light bolt, buffer spring, and buffer will do the trick while giving less fatigue to the other important components?

These days, we can now control gas pressure better with Adjustable Gas Blocks, for instance, like those by Syrac Ordnance, and additionally use light-weight BCG by JP or Young, and incorporate low-mass buffers and springs.


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