Someone school me on adjustable gas blocks and suppressors

[kdunn]

I am about to start my first SBR build and will be doing it in a 300 blackout. I will be running this gun suppressed most of the time and have read a lot about using adjustable gas blocks with suppressors. However I have no experience with adjustable gas blocks and was hoping someone could enlighten me on how they work and why they are beneficial when using suppressors. Any and all information on this topic is appreciated.

 

[243winxb]

Find more info at www.ar15.com by Google " adjustable gas block and suppressor AR15.com " Hornady has this posted

Superformance and Suppressors

The use of suppressors on rifles creates yet another dynamic in firearms design that is not commonly understood or communicated. Consider the suppressor on a firearm the same as a muffler on a car. The suppressor works as a filter for the gas (noise) that is escaping the barrel during firing. As a “filter”, it takes longer for the gas to leave the confines of the firearm, and thus, it creates back pressure. This back pressure, ESPECIALLY in a gas operated firearm forces an extensive amount of gas back through the firearm’s operating system that may create too much thrust too early during the firearm’s cycle of operation.

To counteract this back pressure, the use of an adjustable gas system is advised. By metering the gas system to ensure that it will cycle the firearm correctly and not flood the system with gas/pressure, the gun will work properly and will still benefit dramatically from the increased velocity potential of Superformance ammunition.

http://www.hornady.com/ammunition/superformance-in-gas-operated-firearms

 

[LocoGringo]

Things to consider when looking at/buying an adjustable gas block: how adjustments are made, materials used, how adjustments are "locked", will it fit under an extended handguard (if using an extended handguard), access point (side or front). I've got several different models ranging from a PRI to a Syrac Gen I to a SLR Rifleworks. I can recommend a SLR Rifleworks without hesitation and have heard that a Syrac Gen II is similar in design. Don't try to go "cheap" because you will likely regret it at the worst time.

The post above pretty much covered the "why" of using adjustable gas blocks. A suppressor increases the gas pressure in the system, so an adjustable gas block can cut that gas pressure down so that your rifle won't be so drastically overgassed that it gets beaten up or causes malfunctions. Knowing that, it's important to get the materials correct. The gas block is taking the pressure of high temp. gas, so don't get an aluminum one. It likely won't last very long if you do a lot of shooting.

 

[kdunn]

So by turning the adjustable gas block "up" or "down," you are retaining or releasing gas that is run back through the gas tube and to the BCG? Please correct me if I am wrong on this

 

[Darkbob]

I think it may be more accurate to say that when you adjust the gas block, you are changing the gas port opening. Smaller port means less gas gets through, while larger port lets more gas through.

 

[Singletracker]

So may I ask another question in the same arena? If you go with an Adjustable Gas block will it (or can it) reduce the amount of "blowback"? I was shooting my 5.56 SBR w/Specwar can for the first time the other day. Rifle cycled fine, but I noticed a lot of crud coming back at me.

 

[LocoGringo]

Yes, Darkbob is right. If you reduce the size of the gas port by adjusting the gas block, you reduce the amount of gas coming through the gas system. This should also reduce the amount of crud coming back at you. All of that stuff coming back at you is a reflection of the overgassed situation you are experiencing. That's basically the purpose of an adjustable gas block. It is one method (of several) to properly tune an AR-15 and one of the best solutions for shooting suppressed.

 

[kdunn]

Great answers guy. Thanks for the responses we've gotten so far.

So when so turning the gas block "down" (reducing gas in system) affect accuracy or the function of the gun? Or is it just to allow better functioning with the increased pressure from a suppressor?

 

[Elkins45]

I have a 16" gun and a 10" one. The 10" is only run suppressed with subsonic loads and it doesn't take much powder to make it run.

The 16" is used for medium to full and I absolutely can't stand to shoot it suppressed. I'm a lefty and about 10 rounds is al it takes for my face to be black and my lips to taste like bullet lube for hours. You would need a full face shield to shoot a full mag. That gun will be getting an adjustable gas block soon.

 

[LocoGringo]

Great answers guy. Thanks for the responses we've gotten so far.

So when so turning the gas block "down" (reducing gas in system) affect accuracy or the function of the gun? Or is it just to allow better functioning with the increased pressure from a suppressor?

Accuracy, not likely, but function yes. There is a point that you can turn the gas down so low the rifle won't cycle. When that happens, turn it back up about 1/4 to 1/2 turn and you should be good.

A great way to know if it is cycling properly is to look for the ejected brass. Ideally, it should be piling up around 3-4 o'clock if looking down the barrel is 12 o'clock and the ejection port is 3 o'clock. Generally, overgassed is sending the brass forward and undergassed is sending the brass way back. You want the brass to kick out to your side.

 

[kdunn]

Got it. Thanks LocoGringo!

 

[Arizona_Mike]

Fill mags with one round and adjust your gas block so that the bolt moves back far enough to engage the last-round-hold-open consistently. Then open it up a bit (usually 1/4 to 1/2 turn) for a dirty gun and other sources of variation. I consider LRHO function to be a better indicator than brass direction. You are likely to find adjustments for suppressed subsonic and unsuppressed supersonic to be close (just go with the higher one). Chances are your suppressed supersonic opening will be significantly smaller and your unsuppressed subsonic (a waste of expensive ammo) will be quite a high setting.

Even with your timing right (chamber not opening prematurely with high bore pressure), the volume of the suppressor acts like a booster and your will get a blast of moderate to low pressure gas back out of the empty bore as that reservoir space empties in both directions. A gas handling charging handle like a Gasbuster or homemade equivalent will help. For my left side charger, I've had to start wearing a kerchief around my mouth and nose to avoid powder burned lips. I call it a kerchief because I went with solid sedate colors and I don't lower my pants

Mike

 

[kdunn]

Thanks Mike! I will try out your method when I first begin tuning!

 

[bikemutt]

This may sound funny but I now use a portable fan (4 D batteries) that I set inside the brass catcher. It's aimed right at the ejection port and keeps the acrid fumes moving anywhere but up my nose and under my safety glasses.

Here's the one I ordered from Amazon: http://www.amazon.com/gp/product/B00BJ3XSIS/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

As an aside, I also use it when shooting my bolt rifles suppressed, just below and left of the suppressor and aimed at it, reduces the mirage effect substantially, or at least delays it on a high round count day.

4 D cell batteries will last months.

 

[wally]

If you go with an Adjustable Gas block will it (or can it) reduce the amount of "blowback"? I was shooting my 5.56 SBR w/Specwar can for the first time the other day. Rifle cycled fine, but I noticed a lot of crud coming back at me.

If the crud blowing back at you is coming out through the bolt carrier then the adjustable gas block can help. But if its the crud that blows out along with the ejected empty case the adjustments will make little difference.

I've never felt the need for an adjustable gas block. Invest in nice wrap-around shooting glasses.

I do like the heaviest buffer the gun will run with to help minimize the gas that blows out along with the ejecting empty case -- helps me get more rounds without cleaning.