Is there a trick to making sure gas block and gas tube are installed correctly?

[Garet Jax]

Hello all,

I built an AR sometime ago and have made a couple of trips to the range to test it out. All 3 trips have ended with the BCG not resetting with only 1 round in the magazine. I have opened the Aero adjustable gas block wide open. I have also changed the gas tube to make sure it wasn't the issue:

The BCG will go back far enough to eject the shell, but not far enough to load the next round or to lock open (if only 1 round is left in the mag). It is very hard to fix since I can only fire it at the range so I have to bring it home, make changes and return to the range. Are there some tricks to increase my chances of getting it right?

I am using:

1) Aero Precision .625" Adjustable Low Profile Gas Block
2) Bravo Company Manufacturing BFH 5.56 NATO 1:7 Mid-Length Enhanced Lightweight AR-15 Barrel - Stripped .625 - 16"

 

[outrider58]

Have you tried a different BCG? Do that before going after your GB(it's easier). Sometimes, gas keys leak like a sieve. Ask me how I know. If it still does it with a known functional BCG, then yeah, probably the other end of the gas system needs looking at.

 

[mvee]

It sounds like it is not getting enough gas.

I had a rifle length upper that had the same symptoms. It turned out to have an undersized gas port drilled in the barrel.

I wonder if the adjustable gas block is prone to leaking more gas.

 

[Garet Jax]

Have you tried a different BCG? Do that before going after your GB(it's easier). Sometimes, gas keys leak like a sieve. Ask me how I know. If it still does it with a known functional BCG, then yeah, probably the other end of the gas system needs looking at.

That's a good idea. Will try that. There is a dimple on the bottom of the barrel and I have been lining up the gas block screw with that dimple. I have been using the same screw because otherwise the gas tube protrudes too far into the upper (IMO).

 

[Garet Jax]

It sounds like it is not getting enough gas.

I had a rifle length upper that had the same symptoms. It turned out to have an undersized gas port drilled in the barrel.

I wonder if the adjustable gas block is prone to leaking more gas.

Is there a standard sized hole that should be in the barrel? From what I can see the diameter of the hole is much smaller than that of the gas tube.

 

[outrider58]

It sounds like it is not getting enough gas.

I had a rifle length upper that had the same symptoms. It turned out to have an undersized gas port drilled in the barrel.

I wonder if the adjustable gas block is prone to leaking more gas.

Most newly installed GBs leak until they self seal with carbon. It should not be so bad as to keep the gun from functioning though. It's always best to check the easy shit first, then go on to the harder solutions.

I've had poorly sealed gas keys cause this problem. Remove the key, hone its base, reseal the key/carrier interface, and properly torque and stake the correct gas key screws.

 

[outrider58]

Is there a standard sized hole that should be in the barrel? From what I can see the diameter of the hole is much smaller than that of the gas tube.

No. It all depends on the caliber and length of gas system.

 

[clandestine]

A cheap teslong bore scope will work to check alignment,

Tha adjustable you picked is not one of the better choices for an adjustable.

Adjustable gas blocks are leaky. They can cause a properly functioning gun with a fixed gas block to malfunction once an adjustable is installed.

Adjustable gas blocks need extra gas to overcome inefficiency and to gain maximum function of the adjustable system throughout its adjustment range.

 

[brianns]

Have you tried a different BCG? Do that before going after your GB(it's easier). Sometimes, gas keys leak like a sieve. Ask me how I know. If it still does it with a known functional BCG, then yeah, probably the other end of the gas system needs looking at.

I 2nd this. After trying so many things on my 6.8SPC AR it appears a replacement BCG corrected the bolt hold open 'deficiency' or lack of full hold open on last round. The build started with an adjustable gas block I thought would be neat to have. Now I'm going to try an Aero Precision adjustable one with ball detent adjuster. I'm doing this now hoping the gas is adequate and maybe adjustability might work usefully.

I missed trying a known 'good' bcg with the bolt in the rifle. I kept swapping the parts into known other rifles to test. But I missed trying another bcg in the actual problem rifle. It began working normally. I contacted the manufacturer with my results and they sent me a new BCG.

 

[jrumann59]

I echo Chad's recommendation for a bore scope. Teslongs are pretty good price on Amazon.

 

[inkd]

The Teslong bore scope I bought off Amazon was some of the best money I ever spent on AR tools.

I would also go to a fixed gas block. I had adjustable blocks installed on a couple of mine and wish now that I had just left them alone.

 

[outrider58]

I echo Chad's recommendation for a bore scope. Teslongs are pretty good price on Amazon.

Occam's razor. Check the easy chit first. In my example, I did all the other things including bore scope until the only answer left was the BCG. Bingo!

 

[jrumann59]

Occam's razor. Check the easy chit first. In my example, I did all the other things including bore scope until the only answer left was the BCG. Bingo!

I was just stating that a borescope is good investment for ARs, I do not know how much a gunsmith will charge to check a rifle but I guess at minimum 2 gunsmith visits would pay for a bore scope

 

[Garet Jax]

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Hello all,

Thanks a bunch for the responses. I was able to get back to the range today. The problem seems to be the adjustable gas block. I replace it and the attached gas tube with a regular gas block and the rifle started to work like a champ. I have a feeling that if I was to make the hole in the barrel a little bigger, I could get the adjustable gas block to work. Truth is I got it because I thought it would be cool to have. Not so cool now.

 

[Garet Jax]

A cheap teslong bore scope will work to check alignment,

Tha adjustable you picked is not one of the better choices for an adjustable.

Thanks. Which adjustable gas block would you recommend?

 

[outrider58]

Thanks. Which adjustable gas block would you recommend?

SLRs are good and so are Superlatives, I my opinion.

Most gas blocks have very wide ports. Barrels gas ports can vary widely. If you suspect a barrel's gas port is too narrow, you can open it up more. Do the homework and read up on it before proceeding. Adjustable gas blocks can only restrict gas. They can not add gas beyond what the barrels port will allow.

 

[inkd]

Thanks. Which adjustable gas block would you recommend?

I have SLR's on mine and like them. But, if your rifle is working with the fixed gas block that is on there, I don't know if I would screw with it. To get the adjustable to work, it sounds like you are going to have to open the port. You will be over gassing the gun to turn around and restrict the gas all over again.

 

[clandestine]

Thanks. Which adjustable gas block would you recommend?

I currently use SLR in a few of my AR's.

I have seen many problems with Superlative. I have several examples that I show students. When they carbon up they don't always bleed gas consistently.

Adjustables are a failure point and most require tools and maintenance. Many people don't maintain them properly.

 

[clandestine]

Hello all,

Thanks a bunch for the responses. I was able to get back to the range today. The problem seems to be the adjustable gas block. I replace it and the attached gas tube with a regular gas block and the rifle started to work like a champ. I have a feeling that if I was to make the hole in the barrel a little bigger, I could get the adjustable gas block to work. Truth is I got it because I thought it would be cool to have. Not so cool now.

Stick with fixed gas for that upper unless you have # bits and a jig to ensure the port is drilled straight.

 

[trickg]

Thanks. Which adjustable gas block would you recommend?

Why does it have to be adjustable? Just curious.