AR-15 Gas Issues! Attention AR Docs!

Status
Not open for further replies.
Mot45acp

Mot45acp

Member
Joined
Oct 28, 2005
Messages
1,751
Location
TX
Having the blues on recently built AR. Problem is this was supposed to be my flagship AR.

Problem: I am getting a random issue of failure to lock back after last round. Compounded by it being totally random and unable to duplicate intentionally. About every 3-5 magazines I get this failure. No other cycling issues.

Other symptoms of note:
-Ejection is about 1:30-2:30 with brass bouncing off deflector. Indicating over gassed.
-Ejection is weak, hitting the ground about 3 feet away, indicating under gassed.
- Ejection pattern and strength does not change when swapping buffer weights, buffer springs, bolts or carriers. Suppressed and not show no difference.
-Recoil is normal, not notably sharper or weaker than a standard middy.

All parts are new.
Build Specs:
-Barrel: 16" mid-length Noveske N4 light barrel with pinned gas block. Research shows Noveske runs a little over gassed, but nothing more than H2 is usually needed.
-BCG: Ranier Arms nitride. Gas rings and key all good to go. Black insert and O ring on extractor.
-Buffer set up: Geisselle Braided 42, with both H1 and H2 weights.
-Bolt Release: Strike Industries. Moves freely and engages when manually cycled on empty mags. No BAD lever or anything hanging off it.

What I have tried so far, doing so one at a time.
-Different ammo. All ammo has been brass cased mil-spec or better that has always been solid performers in other ARs.
-Different mags. All quality mags that have been good in other rifles. AR mags are cheap, I toss any that don't function.
-Buffer weights. With the super 42, I tried H1&H2. Then tried Spikes ST-T2 which on my scale is between H1&H2, with a standard buffer spring. Have not tried standard carbine buffer yet.
-BCG was swapped with a BCM, and another Ranier Arms.

Things I've checked.
-Gas block has no notable leaks.
-Gas tube is straight and center. No unusual wear on gas key make up. Pinned into gas block properly.
-No unusual wear on BCG, gas key is properly staked.

So...what the heck am I missing here?
Thanks in advanced.
 
Have you rechecked your gas block alignment? Measured the gas block face to port and then measured the barrel from shoulder to port to make sure everything is properly aligned? I may be way off base on this one, but it sounds to me like you might have a loose block which is hit or miss on if it is properly aligned when firing...even with it being a high dollar part it might be a bad one...it happens to everybody. Also take the empty mag locking arm out and check for any signs of dragging in the pocket. Something is funky, and those two items would be my first places to check. Lube that empty mag lock pocket before reinstalling that part just for good measure,and while it’s out make sure it’s not tight to the pin that holds it in place.
 
Gas block and tube is pinned and centered.

Mag catch moves freely, no dragging. Only other complete upper I have right now is for my SBR, so I can't put it on this lower to check. I may be able to cobble one together from parts.

Haven't done enough testing on this upper with sbr lower yet.

Generally what I do is take 10-15 mags with only 3 rounds each to try and pin this down.

It would be so much easier if this wasn't random. I'm at the point where I may have to remove gas block to see where the gas tattoo is. I would prefer not to.
May try standard buffer and H3. I'm having trouble with symptoms showing both over gassed and under gasses.
 
Over and under gas? Could there be an obstruction floating in your gas block or gas tube left over from manufacturing? You said your upper has a rep for being over gassed so maybe that isn't a problem. Sounds like you have covered all the bases. I'd check for a piece of debris in the tube.
 
Ejection pattern is not a reliable indicator of gas drive. Have you tried the upper on a different lower?
 
Check gas block as already recommended. If determined it's over gassed Black River Tactical had a micro tune gas port to make it smaller. Or you could replace with an adjustable gas block. I would call Clint at Black River Tactical and see what he thinks
 
Are you sure the rings on the bolt are not aligned? If they align, you lose a significant amount of gas. This can happen intermittently if they are close to alignment, then they align for a round or two, causing the symptoms you descirbe, then they can un-align and work (though not the best) again causing some of the other symptoms. It can cause conniption fits. It will be worse if one of the rings is missing. (Don't laugh, I've seen it. Soldiers are not always that observant of such things, partticularly the REMF's I dealt with....)
They should be initially set 120 degrees apart (forming an equilateral triangle), making it less likely for them to align and cause gas loss.
 
May have solved part of the problem!

Sitting here with just the lower, going through mags. I discovered on some of the polymer ones, if you pull forward (towards the barrel) on the bottom of the mag, kind of simulating recoil, the back of the feed lips would contact the shelf on the bolt catch stopping function. Not the finger, but the shelf the finger protrudes from. A few swipes with a file and no more hangups, even when trying to force it to hang up.

All in all I went through about 50 pmags, lancer, and troys before discovering this.

Now all that's left, is figuring out if my weak, forward ejection is an issue, even though I having had any FTFs or FTEs
 
entropy said:
Are you sure the rings on the bolt are not aligned? If they align, you lose a significant amount of gas. This can happen intermittently if they are close to alignment, then they align for a round or two, causing the symptoms you descirbe, then they can un-align and work (though not the best) again causing some of the other symptoms. It can cause conniption fits.
Click to expand...
That’s a myth. It doesn’t matter how the gas rings are aligned. If they’re all lined up it won’t affect anything.

https://primaryandsecondary.com/understanding-the-ar-15-gas-system/

I was told that gas ring myth in the Marine Corps, and it appears the myth is still perpetuated by the military. But it’s not true.
 
Gas rings are fine, same issues when equipped with a known good BCM bcg, and BCG from problem gun works fine in my SBR.

No drag marks on top of bolt catch. But I will check for function tomorrow or this weekend. If it can get stuck in the down position, then it's possible it could get pushed partially up causing carrier drag.
 
It sounds like it cycles, but just not enough to consistently lock back after the last round....sometimes.
You already checked everything else that's easy. That it isn't a specific mag. No binding of the bcg. Gas rings on the bolt exist. Visual on gas block and tube. Carrier key on bcg is tight.

I would first try a standard carbine buffer. It may not be as overgassed as you thought. Remember that 1:30-2:30 ejection direction doesn't matter if it's only ejecting 3ft away.

Probably not what you want to hear, but most of the cycling problems I have had to deal with were a direct result of the gas block, the gas tube, or the carrier key.

If you haven't solved it by now, I would still tap the pins out of the gas block, remove bcg and ch, slide gas block forward to confirm carbon buildup centered at gas port location and to give room to run a pipe cleaner down the gas tube to check for or loosen up any debris and do the same thing to the carrier key. Since it's pinned, there are no concerns about re-installing the gas block to the previous location, except to make sure the tapered pins are re-installed in the orientation they were removed. It's probably not necessary to remove the muzzle device.
 
UPDATE!

I caved and sent whole upper off to Noveske. They received it yesterday, and today called me. They said the carrier key, while tight, was leaking badly. They swapped it out and now it's good to go. Shipping back today.

Pros:
Fast turnaround.
It wasn't their carrier, so I offered to pay, they still declined. Basically warrantied a part that wasn't even theirs and covered return shipping. That's customer service!

Con (not really a con per se)
I tried 2 different know GTG, quality carriers and had same problem. :thumbdown:
This is in no way accusing anyone of anything, just perplexing.
But if it works now, I am a happy customer. Will update when I receive it and shoot.
 
Two things here strike me as odd. First, it’s a little odd that a company — even one with good customer service — would warranty a part that wasn’t even theirs. And it’s very odd that you tried two different quality carriers and had the same problem with both: With quality companies it’s unlikely to get a gas key that leaks enough to cause problems, let alone two successive ones.

I suppose there are two possibilities here:

1) You just got really unlucky and happened to get two bad carriers, and Noveske went above and beyond by both paying for a replacement part and shipping it back for free, even though the problem was with a competitor’s part and not theirs.

2) The problem wasn’t actually the gas key and they actually did something else to fix the upper and didn’t want to admit that it was their fault, but they still decided to make it right by not charging you.

I guess we’ll never know which it is, but as long as it works now I guess it doesn’t matter all that much.
 
I'm curious as well.
The BCG's I tried were pulled out of other guns that run great, including a 11.5" that I run hard, suppressed, small carbine courses etc.

But if I get it back and all is well, then I have no complaints. It's just the mechanical side of me likes to find root problems and figure out how to prevent them in the future.
 
Could it have been the end of the gas tube was a little undersized and that was where the leak was happening? That would explain why 2 other carriers that were known to be good also showed the same symptoms. When you assembled the rifle...did you check the fit of tube to key? Just curious....
 
I don't know how to check that. Other than a visual allignment check that the carrier didn't move the gas tube to one direction. It fit on there snug, comparable to my other ARs. But its definitely a possibility. They didn't say where the leak was from, I assumed it was between the carrier and key, but didnt think to ask. That is a good point.
 
Got it back from Noveske. It is better...ish, but barely. This thing is waaaaay overgassed. It now ejects about a foot further then before. Still light primer strikes. Still 1 o clock ejection. Only difference is suppressed does 1230 ejection now. I think bolt bounce may be the issue.

Based on this experience in quality, and warranty I will not use noveske products anymore. This was supposed to be a premium build, using the highest quality parts, and I have never had the problems experienced with this build.

I have a additional weight to convert buffer ro H3 on order. I dont want to use adjustable gas block, but I may be forced to.
 
If it is over gassed (ejection pattern is an iffy indicator at best) an H3 buffer will not fix the problem. You can use either an adjustable gas block, or a BRT micro port to reduce gas flow. What diameter is the gas port?

The light primer strikes are likely due to a light hammer spring.
 
Looking at the inserts now.
Hammer spring is good and installed properly. It's a Geissele SSA that came out of my SBR. Uses full strength hammer spring and has never had an issue till now. Even put it back in SBR to rule it out. Functions fine.
 
Status
Not open for further replies.

Similar threads

socalbeachbum
  • Locked
need help choosing heavy buffer & adjustable gas block AR-15
Replies
13
Views
4K
Tomac
T
M
  • Locked
Testing Buffer Weights and Gas Flow
Replies
9
Views
1K
MistWolf
M
A
  • Locked
Is there a valid reason to use a heavy buffer with an adjustable gas block.
Replies
5
Views
3K
C-grunt
C-grunt
G
  • Locked
AR Gas Enigma
2
Replies
39
Views
2K
Coal Dragger
C
N555
  • Locked
The H5 carbine buffer for suppressed guns
Replies
0
Views
248
N555
N555
Back
Top