Problem with new AR- gas block?

[IndyIN]

I’m an AR newbie, and wanted to see if anyone had ideas to offer about a problem I've experienced. Recently purchased a complete 16” upper from Aero, and took it to the range today. It shot well for about 20 rounds, and then would not extract. It wasn’t feeding a new round, so it made me think it was short stroking. I had another AR with me, and I swapped BCGs just to test. Same issue with the Aero, and no problem with the other AR.


I didn’t swap uppers at this point as we were running out of time, but when I got home I noticed what looks like leakage around the gas block (front and back). Is the gas block the likely culprit based on the photos? Any thoughts as to the problem would be greatly appreciated.

 

[NyleRN]

Since you tested another known working BCG then you've eliminated the possibility of a faulty gas key. Seems if it functioning for 20rds then went south sounds like the gas block could have came loose. It's not uncommon to have some carbon blow by around the gas tube where it enters the block. It usually seals up with carbon. Take the rail off and see if the block is tight. Start there

 

[IndyIN]

Since you tested another known working BCG then you've eliminated the possibility of a faulty gas key. Seems if it functioning for 20rds then went south sounds like the gas block could have came loose. It's not uncommon to have some carbon blow by around the gas tube where it enters the block. It usually seals up with carbon. Take the rail off and see if the block is tight. Start there

Thanks for the quick response. Does the amount of blow by look pretty typical to you? It looks to be all around the block itself vs where the tube enters the block.

 

[Fizzerpilot]

I've installed a few blocks, never seem that much blow off

 

[NyleRN]

Thanks for the quick response. Does the amount of blow by look pretty typical to you? It looks to be all around the block itself vs where the tube enters the block.

Now that I look at the pics a little better than before when I originally posted(watching the seahawks patriots game) I see that the carbon is in front of the block on the barrel. I'd still pull the rail and see if the block is loose. In my opinion I don't think it should have that much blow by where it is

 

[IndyIN]

I'll pull the rail tomorrow and see what I can figure out. I can get to the gas block screws when I remove the fore grip, so I'll give that a try first. From what I can tell I shouldn't really torque them down, but they should be tight. Is that the right way to go?

 

[TJ Kackowski]

Since you purchased a complete upper from Aero, give them a call to see how best to proceed. If the upper is under warranty, you might as well take advantage of it.

 

[rvb]

Not much to go on, but from this picture (the muzzle is to the left, correct?), it looks like behind the gas block there is a BIG, like 1/4" offset from the "shoulder" on the barrel? This is usually in the 0.03" range. If the block is not pinned or dimpled for set screw, or over-oiled as it appears to be if it's a clamp-on, it may have walked forward under recoil, so the port in the barrel may not be lined up with the hole in the block.

-rvb

 

[rvb]

I had another AR with me,

also, since you have another AR, take the uppers off the lowers, remove the BCGs, and look into the upper receivers from the bottom. Look at how far the gas tubes protrude into the receivers. If I'm right above, I bet your working AR's tube sticks into the receiver farther. Being that far forward, it's -possible- interference between the tube and carrier drove the tube/block forward.

-rvb

 

[IndyIN]

also, since you have another AR, take the uppers off the lowers, remove the BCGs, and look into the upper receivers from the bottom. Look at how far the gas tubes protrude into the receivers. If I'm right above, I bet your working AR's tube sticks into the receiver farther. Being that far forward, it's -possible- interference between the tube and carrier drove the tube/block forward.

-rvb

Hi Ryan,

I compared uppers, and you are correct... the Aero gas tube is significantly more forward than my M&P. If the carrier drove the gas block forward, I would sort of expect to see the gas tube mangled/bent (it could be, if I compared it to a new one). I was able to tighten it up a little, but the screws were not falling off either. Would you expect to see damage to the gas tube if the carrier forced it? I'm wondering if it was a case of the gas block not being tight, and 20 rounds later it worked its way far enough forward that it stopped cycling?

I'm sort of inclined to send it back and let Aero figure it out.


M&P




Aero

 

[Huntinfool]

Probably best to let Aero deal with it, due to warranty. Unless that isn't important to you.

 

[IndyIN]

I submitted a trouble ticket via Aero's website, and got a response quickly. Happy to send me a shipping label, but also documented that it was fine for me to re-set it myself and not impact any warranty.

I decided to stop being miffed and just fix it myself a few min ago. If it doesn't hold, I'll send it back. I appreciate all the suggestions and help.

 

[sig1473]

Get a gas block dimpling jig. I got one from these guys and it works well.1B Gas Block Dimple Jig B 0.500" Centers (PRI, Syrac, Aero Precision, Ballistic Advantage, Superlative Arms) | BRD ENGINEERING Dimpling your barrel is easy when you have the right tools.

 

[Huntinfool]

let us know if that fixes it.

 

[rvb]

Hi Ryan,

I compared uppers, and you are correct... the Aero gas tube is significantly more forward than my M&P. If the carrier drove the gas block forward, I would sort of expect to see the gas tube mangled/bent (it could be, if I compared it to a new one). I was able to tighten it up a little, but the screws were not falling off either. Would you expect to see damage to the gas tube if the carrier forced it?

I'm wondering if it was a case of the gas block not being tight, and 20 rounds later it worked its way far enough forward that it stopped cycling?

that's exactly what it was. I only mentioned the tube/key interface since most of the time a loose block walks backwards, not forwards. (of course, there's lots of variables there in ammo and gun setup. but the bolt hitting forward is a sharper impulse than the recoil pushing the gun back). so long as the tube and the key look ok, I wouldn't worry about it. It may have just been they weren't aligned all that well.

make sure the block is centered left/right. put a 0.030 gap (about 1/32") between the block and the barrel "shoulder," tighten down good, and it should run. if it still gives you problems, I'd send it back (have them pin it if it's a clamp on, or add a dimple if it uses set screws).
I'd loosen it up first and take some brake cleaner and get as much of that oil off between the barrel and block as you can.

once you have the gas block tight, slide the carrier into the upper and see how smoothly the tube enters the key. very slight bends, usually just in the section outside the upper, can help things line up inside the upper. you don't want to really feel the key/tube hit, just a little resistance.

-rvb

 

[gmcttr]

...put a 0.030 gap (about 1/32") between the block and the barrel "shoulder,"...

Unless the gas block is not designed for use with a handguard cap in which case it should be placed tight against the barrel shoulder. Ask Aero which type gas block you have.

 

[rvb]

Unless the gas block is not designed for use with a handguard cap in which case it should be placed tight against the barrel shoulder. Ask Aero which type gas block you have.

someone makes one like that? always someone muckin with the system....

every one I've ever used had an offset. I measure/blueprint out the hole locations on the barrel/block and calculate the spacing to center up. It's almost always right around .030. I use feeler gauges to set it where I want before tightening. I guess that's why I go through the hassle, never know when you'll see something "oddball."

-rvb

 

[NyleRN]

It shouldn't matter if the block is flush against the shoulder. The port in the block is almost twice the diameter of the barrel port. Even when against the shoulder there's no overlapping of the ports. I promise

 

[rvb]

It shouldn't matter if the block is flush against the shoulder. The port in the block is almost twice the diameter of the barrel port. Even when against the shoulder there's no overlapping of the ports. I promise

I promise that's not always true.

In fact, about 2 weeks ago I had it actually happen to me for the first time ever... the clamp-on block on my 308 moved from where I had it set back against the shoulder, and it quit working. I put 0.30 gap back in and it worked again (ive since been reading that company supplies junk screws that stretch w/ their block)

~2x the diameter is only true in certain cases, eg carbines w/ .060-.065-ish ports, you might get away w/ it there depending on how well everything is cut. I recall somewhere around .090+ on a rifle port to into ~.120 on most blocks, i.e. def not 2x. going from memory so can't recall exactly. but that says you'd get 0.015+ overlap when pushed back...

plus pre-dimpled barrels usually assume the ports directly lined up to center the set screw, so you get best contact w/ the gap, regardless of alignment.

for the OP, all this is into the minutia. push it back or leave a gap, whatever... try it and see, or call the manufacturer and see what they say.

-rvb

 

[sig1473]

Like I said before, get a gas block jig. The top screw goes into the gas port and the bottom part of the jig is exposed so you can drill your dimple so your gas block is perfectly aligned. I've used it many times for my ARs and others. Only costs $65.