Assistance with under-gassed ar15 build?

[Member 34319]

Seems like I have some type of gas blow-by on one one side of the gas block, going forwards towards the muzzle. Thoughts?


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You slid that gas block on. It wasn't welded in place. It isn't an airtight fit.Therefore some leaking gas is expected in a new build. It will eventually build up enough to stop leaking. In other words this is normal. It also leaks at the gas tube some. 40-50 thousand PSI will find its way.

 

[P7M13]

If you're implying that it's an adjustable gas block with bleed-off, you are incorrect.
OP, most gas blocks take some time to seal up, depending on fit. That one looks excessive, but will probably still seal.

Some amount of bleed is normal, and that doesn't look like it should cause your problem. But, it may.
I did experience one case where bleed/leak like that severely affected my accuracy. I replaced the pinned factory block with a set screw one, and the 3moa gun became 1moa.

 

[titsonritz]

Those barrels have a notch on the barrel and a tab on the gas block for alignment.
The gas port size is listed at .076", perfect for a 16" middy and should run well with a blue spring and H buffer or an A5H2 buffer and green spring.

A new pin is probably 50¢ from Tacoma Screw, drive it out, scoot the GB back a bit and measure the port.
You'll be able to see if the notch is directly behind the gas port also and not off to one side or the other.
They are a solid company, I'd be surprised if something is out of spec but anything is possible.
At any rate I'm certain they will take care of it if something is goofed up.

Which is why I'd doubt it is an alignment issue.

I agree, there is nothing wrong with that GP size, all my 14.5"-16" mids use that size, which I verified. I don't all my tools with me but I do have my pin gauge set if you would to bring it to Oregon City we can measure it.

My first question would be what ammo are you using? That barrel is optimized for use with MK262 (Black Hills 77gr equivalent). If you are not using full power NATO spec ammo it may be an issue.

ETA: I have plenty of gas tube replacement pins on hand, you are welcome to a couple.

 

[ma96782]

Perhaps.......
This might be a lesson, to buy a "completed upper"?

Nah.....

Aloha, Mark

PS.....for the testing......are you using "full power military spec factory ammo" vs. "reloads (or other ammo)" that might be somewhat under powered"?

 

[helloyatches]

Check your rings

 

[titsonritz]

Check your rings

For what? This is a new BCG.

 

[titsonritz]

I have no first hand knowledge but I have heard several instances of people running the super42 and h1 kit and immediately getting short stroking.I like extra parts anyway so I would buy the most basic standard cheap spring and buffer and see what happens. You might also want to YouTube some school of the American rifle for quick easy bcg checks.

Changing out to a standard carbine spring and carbine buffer would be an easy first step.
Also, be using full power ammo for your troubleshoot.
M855 or similar.

This would be my next step. I am not sold on those G parts at all.

 

[kmk1012]

My sons newly assembled AR is having similar issues, seems way undergassed. It's short stroking and leaving the fired case in the chamber without enough force to extract. I'll be checking out some of those videos to try and get it running before our trip east in two weeks.

 

[CharlesAFerg]

Perhaps.......
This might be a lesson, to buy a "completed upper"?

Nah.....

Aloha, Mark

PS.....for the testing......are you using "full power military spec factory ammo" vs. "reloads (or other ammo)" that might be somewhat under powered"?

aguila 62gr (mexican military ammo) & winchester 55gr factory ammo

 

[CharlesAFerg]

Check your rings

Holds the bolt up just fine standing on bolt face.

 

[msgriff]

Here's a live fire short stroke test that's fairly reliable. It should be done using a sled, bags, bipod or tripod as attempting it freehand can be dangerous due to loss of control when firing. This test is more for consistent failures, such as 1 failure in 3 (or more frequent), and you do the test around 2x the frequency of failure (i.e. 1 failure in 3 = 6 test cycles).

Manually lock the BCG back and return the charging handle forward to latch. Load 1 round in a mag and insert mag. Pull down on the mag to make sure the mag catch is engaged. Push the bolt release to charge. While pushing hard on the lower portion of the bolt release lever with your thumb (same as manually engaging the bolt catch), fire the 1 round. If the BCG doesn't lock back, it's short stroking due to the gas system. If the BCG does lock back, it's can be an issue with the mag/mag spring, the bolt catch spring, or more common with large frames, over-speed cycling. NOTE: With no mag and an empty chamber, push the lower portion of the bolt release lever while cycling the BCG with the charging handle. This will give you a slow-motion idea of how it feels and what to expect when doing the actual live fire test.

 

[P7M13]

Check your rings

Holds the bolt up just fine standing on bolt face.

Yah, when I had to replace rings, I got considerably more gas on ejection than normal. On one of my 6.8's, the rings are getting to the point of needing replacement, but it still runs well.
When you pull back on the bolt, does it lock back without excessive force? A I've had clearance issues that interrupted cycling and things like that.

 

[CharlesAFerg]

Update on this: Swapped the bcg with a known working bolt and the gun ran great. Interesting.. Bolt with the issues is a new Aero standard bcg.

 

[ma96782]

Aloha, Mark

 

[powermad]

Update on this: Swapped the bcg with a known working bolt and the gun ran great. Interesting.. Bolt with the issues is a new Aero standard bcg.

Good deal.
I haven't owned a lot of AR's but the BCG seems to be the most problematic.
I would rather pay a little more for a quality made BCG and not worry about if it's in spec or assembled correctly.
I'm impressed with Sionics BCG's and will use them from now on, the phosphate one was $20 less than everyone else the last time I looked at $160

 

[bellarum]

Did you take the new (non functioning) BCG apart and clean everything, make sure the ring gaps are offset, lube it up only where necessary and try it again?

 

[edzz]

Update on this: Swapped the bcg with a known working bolt and the gun ran great. Interesting.. Bolt with the issues is a new Aero standard bcg.

Did you swap and test the questionable BCG in the AR that the working BCG came from? BTW thanks for the update.

 

[CharlesAFerg]

Did you take the new (non functioning) BCG apart and clean everything, make sure the ring gaps are offset, lube it up only where necessary and try it again?

Yes, I previously made sure the rings were staggered. two of them weren't the first time I tested it, but the malfunctions still occurred while they were staggered.

 

[CharlesAFerg]

Did you swap and test the questionable BCG in the AR that the working BCG came from? BTW thanks for the update.

Nope, but I will next time.

 

[solv3nt]

My wife always complains that I'm over-gassed.