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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
Does anyone know what their gas port diameter is? A .0935 chucking reamer fits tightly in mine (20" satern). This is on the larger end of 5.56 gas port sizes but my rifle acts like it's just on the borderline of being under gassed. I'm presently running an AR-15 carrier, carbine buffer (3oz) and carbine spring. When I tried a heavier buffer or even just an M-16 carrier the spent case would eject but the bolt would not pick up the next round or lock back on an empty magazine. On rare occasion I get a failure to feed and it cost me a follow up shot on a pack of hogs last year. Other than opening up the gas port what else should I looks at or consider?
Trying to diagnose a potential gas issue - LRRPF52 - 03-27-2012
The same symptoms exhibit if you're over-gassed and under-gassed, since the gas rushes too fast out through the vent holes on the Bolt Carrier before enough inertia has been imparted to the carrier.
What bullet weights is this happening with?
If you had an adjustable block, you'd be able to tell right away if your gas port/system balance is under-gassed or over-gassed. There is a curve with the outlying margins both not having enough gas.
I would try an adjustable block before cutting the port. You could also do both.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
LRRPF52 Wrote:The same symptoms exhibit if you're over-gassed and under-gassed, since the gas rushes too fast out through the vent holes on the Bolt Carrier before enough inertia has been imparted to the carrier.
What bullet weights is this happening with?
If you had an adjustable block, you'd be able to tell right away if your gas port/system balance is under-gassed or over-gassed. There is a curve with the outlying margins both not having enough gas.
I would try an adjustable block before cutting the port. You could also do both.
I was shooting 123 SMKs a couple of weekends ago when I tried swapping carriers. Most of my brass was landing 4:30-5:00, maybe a little further back with the M-16 carrier. I while back I did the same test with 100 grain bullets and got similar results.
An adjustable gas block is on the list of possibilities. I really don't want to ream the port if I don't need to but I have a .0980 reamer if I decide to. This rifle has functioned flawlessly 99.5% of the time (if you don't count the bad reloads I had on the helo hunt
) and the malfunction I mentioned above could have been due to the mag not being seated or something else. I just seems strange that most everyone else is running M16 carriers and/or H3 buffers and mine won't run with them.
Trying to diagnose a potential gas issue - LRRPF52 - 03-27-2012
It does sound like your port would need opening based on what you've said, but I would still use an adjustable gas block no matter what you do. If the system was workign fine with your loads, I would say leave it alone, but if you are having short-stroking, it needs diagnosing and fixing. This could be exascerbated by low temperatures, but I'm not sure what temps you're shooting in.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
Here's something else I just noticed. The gas tube that was in the Grendel is on top. Diameter is .165". Gas tube on the bottom was in another AR. Diameter is .177". Could the smaller gas tube be leaking too much gas from the carrier key?
[ATTACH=CONFIG]1096[/ATTACH]
Clarification: diameters listed above are OD at the tip of the tube.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
LRRPF52 Wrote:It does sound like your port would need opening based on what you've said, but I would still use an adjustable gas block no matter what you do. If the system was workign fine with your loads, I would say leave it alone, but if you are having short-stroking, it needs diagnosing and fixing. This could be exascerbated by low temperatures, but I'm not sure what temps you're shooting in.
Temps were in the 70s. I really hate to mess with it but it does seem to be just south of 100% reliability border.
Trying to diagnose a potential gas issue - Drifter - 03-27-2012
Maybe I missed it, but what ammo?
Light bullets and / or faster burning powders in a rifle-length gas system can sometimes suffer reliability issues.
But the AR-15 carrier with standard buffer and spring that you're using should help.
Trying to diagnose a potential gas issue - Variable - 03-27-2012
txgunner00 Wrote:Here's something else I just noticed. The gas tube that was in the Grendel is on top. Diameter is .165". Gas tube on the bottom was in another AR. Diameter is .177". Could the smaller gas tube be leaking too much gas from the carrier key?Possibly. I don't have any gas tube data available, but I've never seen one like the tube on top. I've always seen tubes like the one on the bottom....
[ATTACH=CONFIG]1096[/ATTACH]
Trying to diagnose a potential gas issue - Bwild97 - 03-27-2012
My gas port measures .105 and my gas tubes ID is .115, my tube is similar to the tube on the bottom as well.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
Variable Wrote:Possibly. I don't have any gas tube data available, but I've never seen one like the tube on top. I've always seen tubes like the one on the bottom....
That's why I brought it up. I used to seeing the shape on the bottom and I didn't pick up on the difference until yesterday.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
Bwild97 Wrote:My gas port measures .105 and my gas tubes ID is .115, my tube is similar to the tube on the bottom as well.
Thanks. What length barrel/ gas system?
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
Drifter Wrote:Maybe I missed it, but what ammo?
Light bullets and / or faster burning powders in a rifle-length gas system can sometimes suffer reliability issues.
But the AR-15 carrier with standard buffer and spring that you're using should help.
100-123 grain bullets. 8208.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
I added a clarification to the gas tube picture. The measurements listed are OD of the tube at the tip.
Trying to diagnose a potential gas issue - Variable - 03-27-2012
txgunner00 Wrote:That's why I brought it up. I used to seeing the shape on the bottom and I didn't pick up on the difference until yesterday.
Yeah, you might be losing some pressure by the loose fit with your gas key. I'd just replace that tube first and see what happens. Of course I say that because I'm a cheap skate with a couple extra tubes in the parts box.LOL
Trying to diagnose a potential gas issue - LRRPF52 - 03-27-2012
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.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
Variable Wrote:Yeah, you might be losing some pressure by the loose fit with your gas key. I'd just replace that tube first and see what happens. Of course I say that because I'm a cheap skate with a couple extra tubes in the parts box.LOL
I did that late last night. Didn't seem to make much difference but I only fired one round. I'm going to mess with it some more tonight.
Trying to diagnose a potential gas issue - txgunner00 - 03-27-2012
I'm having a heck of a time finding a .875 adjustable gas block. Anyone have any experience with an adjustable gas tube?
http://www.midwayusa.com/product/2979396319/mgi-adjustable-gas-tube-ar-15
Trying to diagnose a potential gas issue - LRRPF52 - 03-27-2012
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
Trying to diagnose a potential gas issue - leopard6.5 - 03-27-2012
txgunner00: Midway USA has a PRI adjustable gas block for .875. Unfortunately you also have to buy the gas tube with it as that is how it comes.
Here's the link: 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
Good luck.
Lee
Trying to diagnose a potential gas issue - Bwild97 - 03-27-2012
I have a 24" barrel with rifle length gas system.