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+--- Thread: Trying to diagnose a potential gas issue (/showthread.php?tid=2489)
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
LRRPF52 Wrote:txgunner00,
Your Grendel gas tube "doughnut" is gone...totally worn off, as in, the carrier key has scored it until the doughnut is gone, or someone purposely did it for whatever reason. That could be the issue right there-not enough gas seal. Your tube should look like the one on the bottom of the pic you posted. This happens sometimes when gas tubes aren't perfectly aligned with the barrel nut. Put a new tube in, ensure it is aligned properly.
The way I do it is after an anal visual inspection of alignment through the slot in the upper, I carefully run a bolt carrier without a bolt in it into battery slowly. If I feel any binding, I know the key and doughnut are rubbing against each other. I usually check this because I assemble my own carriers and key myself, to make sure they are unitized with permanent sealant, then torqued and staked.
If I remember correctly the one on the top is the newer of the two gas tubes by several years. I'll double check the alignment just to be sure.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
LRRPF52 Wrote:I have had good experiences with most of the MGI products, but haven't purchased that adjustable gas tube based on the reviews of gas leakage. Here is what you're looking for:
http://www.midwayusa.com/product/992168/pri-low-profile-adjustable-gas-block-with-straight-rifle-length-gas-tube-ar-15-lr-308-standard-barrel-875-inside-diameter-steel-matte
How in the heck did I miss that?:confused::confused: Thanks.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
Bwild97 Wrote:I have a 24" barrel with rifle length gas system.
Thanks.
Trying to diagnose a potential gas issue - CPT.CRAZY - 03-27-2012
I've been looking at adjustable gas systems and saw several reports of the MGI tube braking when tring to adjust the system.
Trying to diagnose a potential gas issue - txgunner00 - 03-28-2012
LRRPF52 Wrote:txgunner00,
Your Grendel gas tube "doughnut" is gone...totally worn off, as in, the carrier key has scored it until the doughnut is gone, or someone purposely did it for whatever reason. That could be the issue right there-not enough gas seal. Your tube should look like the one on the bottom of the pic you posted. This happens sometimes when gas tubes aren't perfectly aligned with the barrel nut. Put a new tube in, ensure it is aligned properly.
The way I do it is after an anal visual inspection of alignment through the slot in the upper, I carefully run a bolt carrier without a bolt in it into battery slowly. If I feel any binding, I know the key and doughnut are rubbing against each other. I usually check this because I assemble my own carriers and key myself, to make sure they are unitized with permanent sealant, then torqued and staked.
I went back and looked at that gas tube again and the "dough nut" was never there. There are still tool marks present were it was turned down. I wish I can remember where I got it.
Trying to diagnose a potential gas issue - txgunner00 - 03-28-2012
Did some more testing tonight. Turns out it's not the gas system at all- it's the carrier. I tried another M-16 carrier and a H3 buffer and got full function. Now I need to figure out what's wrong with that carrier...
Trying to diagnose a potential gas issue - LRRPF52 - 03-28-2012
Mic the inner diameter of the bolt recess that is hard-chromed on both carriers and compare. Are they both M16-weight carriers? Check the carrier key for secure attachment. The carrier keys can come loose when not installed securely, and you won't even notice it most of the time. I used to see this with a lot of carriers from a certain major AR15 maker, and had to correct them at the shop I worked at on a frequent enough basis to know what to look for.
This is why I prefer to build my own carriers from scratch. I select Milspec M16 carriers, chrome-lined carrier keys, and US-made fasteners. I degrease the parts bone dry with hot wash and acetone. Using aviation-grade, temp insensitive sealant, I mate the carrier key to the carrier after ensuring the gas tube is not binding. I also place sealant on the fasteners, torque them to spec, and stake them with my vice-mounted staking tool.
With the amount of heat that is relayed back through the carrier key, carriers without aviation-grade sealant can come loose, even when "properly-staked". Your gas circuit is gone if your key comes loose even slightly, as gas with follow the path of least resistance along its way through the circuit.
Trying to diagnose a potential gas issue - txgunner00 - 03-28-2012
It doesn't appear to be loose but have to check those things tonight. Thanks for the tips.
Trying to diagnose a potential gas issue - txgunner00 - 03-29-2012
I checked for function in 4 different rifles with different bolts. Same issue in all. Visually I can't see anything different from this one to the others I own. Should I just junk it and get a BCM or similar carrier?
Trying to diagnose a potential gas issue - LRRPF52 - 03-29-2012
If the key is loose, it needs to be secured properly to the carrier. If the bolt recess channel is not hard-chromed correctly, or the inner diameter is off, that could cause problems, but it's usually the carrier key fastening, or lack thereof.
Trying to diagnose a potential gas issue - txgunner00 - 03-29-2012
There's no evidence of gas leaking from the key and it seems to be fastened well, at least I can't move it. Any chance the gas ports aren't lined up? A pipe cleaner passes through just like my other carriers.
I don't have a set of inside calipers but I'll try to measure the ID of the bolt channel tonight.
Here's some pics if they do any good.
[ATTACH=CONFIG]1117[/ATTACH]
[ATTACH=CONFIG]1116[/ATTACH]
[ATTACH=CONFIG]1118[/ATTACH]
[ATTACH=CONFIG]1119[/ATTACH]
[ATTACH=CONFIG]1120[/ATTACH]
[ATTACH=CONFIG]1121[/ATTACH]
[ATTACH=CONFIG]1122[/ATTACH]
I took these with my phone so they aren't very good. I can get better ones if it will help.
Trying to diagnose a potential gas issue - LRRPF52 - 03-29-2012
Did you say that this carrier causes the same problem in 4 other balsters? If so, that is weird. I can't see anything out of the ordinary with it, other than it appears that the key is not chrome-lined, but that is just the appearance in the pics. When clean, it is easy to tell a chromed carrier key from a non-milspec carrier key. It is chromed on the inside where the gas tube inserts on a milspec key. I didn't know this for a long time.
Trying to diagnose a potential gas issue - Drifter - 03-29-2012
At a glance, the wear at the base of the key doesn't look the same on each side. Perhaps normal, as I'm not looking at any of mine at the moment, but might be something to double check.
Trying to diagnose a potential gas issue - txgunner00 - 03-29-2012
LRRPF52 Wrote:Did you say that this carrier causes the same problem in 4 other balsters? If so, that is weird. I can't see anything out of the ordinary with it, other than it appears that the key is not chrome-lined, but that is just the appearance in the pics. When clean, it is easy to tell a chromed carrier key from a non-milspec carrier key. It is chromed on the inside where the gas tube inserts on a milspec key. I didn't know this for a long time.
Yes. My 6.5, and a 20", 16" and two 10" .223 uppers. Would it be worth trying to replace the key? I'm pretty sure the key that's on it is not CL.
Trying to diagnose a potential gas issue - txgunner00 - 03-29-2012
Drifter Wrote:At a glance, the wear at the base of the key doesn't look the same on each side. Perhaps normal, as I'm not looking at any of mine at the moment, but might be something to double check.
Noticed that too but my other carriers are the same way.
Trying to diagnose a potential gas issue - LRRPF52 - 03-29-2012
I would try replacing the key with a chrome-lined, TiN, or entire hard-chrome key, as long as the bolt recess chamber is chrome-lined, and within spec for ID. That is one of the most critical dimensions on the carrier.
Another problem that was encountered with a certain maker's carriers was that they were too wide at the raceways, and had a lot of drag in the upper, leading to sluggish cycling, reliability problems. Check the OD of your raceways (the only places where the carrier actually rides in the upper) against the OD of your other carriers.
Those are the 3 areas I would look at first:
Bolt recess ID
Raceway OD
Then carrier key replacement
Trying to diagnose a potential gas issue - txgunner00 - 04-27-2012
Just following up on this...
Turns out one of the cap screw heads was torqued off but staked in place so it didn't come loose. I used an easy-out to remove the broken screw and replaced the key and screws with mil spec parts and it works just fine now.
Trying to diagnose a potential gas issue - noone - 04-30-2012
Whenever I think there is an issue with a gas system on a direct impingement rifle, the first thing I do is replace the gas rings just to make sure that isn't the problem. That little idea has rescued me from frustration many times.
Trying to diagnose a potential gas issue - txgunner00 - 04-30-2012
That's one of the first things I looked at, but this bolt had fewer than 1000 rounds on it. This problem did remind me to check my 5.56 SBR and there wasn't much left of those. Replaced them before they became an issue.
Trying to diagnose a potential gas issue - XcountryRider - 11-15-2013
Anyone know what size hole should a 18in barrel have for a rifle length gas system?