More FTF issues for Me!

[TXBK]

Did you rule out magazine issues, by swapping mags?

[BufordTJustice]

I know, it does seem crazy, but the BCG is literally brand new and has been run in 3 other different uppers. I don't understand how it could just show its flaws all of a sudden. My best guess is that the block and port are out of alignment, but as far as my jigs can tell, it's all perfect. The BCG also seems to seat/close well into the chamber.


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How much, if any, gas leakage are you getting from the gas block journal and the gas tube as it fits into the gas block?

Also, a new BCG does not necessarily mean it is functioning as intended. I've run one burned up gas ring on a bushmaster and it ran 100%. I knew it didn't run in a 6920. A known good brand of BCG is more important than new. What brand BCG are you using? BCM/colt/LMT? Is there any gas leakage from around the base of the gas key? Are the gas rings on the bolt present and in good condition?

Also, it would now be worth pulling the gas block off the barrel and seeing if you're getting a dark circle that is roughly centered (or, at least, not obscured) around the gas port on the barrel. Does the gas block fit resonably snug around the gas block journal of the barrel, or is it loose until you tighten the screws? Also, what brand upper receiver are you using?

[The FNG]

Did you rule out magazine issues, by swapping mags?

Yes, I've tried 2 Pmags and 2 Noveske GI mags.

How much, if any, gas leakage are you getting from the gas block journal and the gas tube as it fits into the gas block?

Also, a new BCG does not necessarily mean it is functioning as intended. I've run one burned up gas ring on a bushmaster and it ran 100%. I knew it didn't run in a 6920. A known good brand of BCG is more important than new. What brand BCG are you using? BCM/colt/LMT? Is there any gas leakage from around the base of the gas key? Are the gas rings on the bolt present and in good condition?

Also, it would now be worth pulling the gas block off the barrel and seeing if you're getting a dark circle that is roughly centered (or, at least, not obscured) around the gas port on the barrel. Does the gas block fit resonably snug around the gas block journal of the barrel, or is it loose until you tighten the screws? Also, what brand upper receiver are you using?

I'm not sure I'm getting any gas leakage from the barrel/ block mating area, but there is some on from the tube. It does not seem excessive, but I can post pictures when I get home tonight. I will pull my BCG apart tonight and inspect along with pictures. It is a carrier I bought from IG, so I don't know the brand, but I would assume it to be quality because it came from him. The bolt is a PSA (I know) but my Noveske BCG was stolen about a month ago when my truck was broken into, so its all I have right now until my new carriers come in (I bought two more from IG and I have 2 bolts I bought from Noveske). I will see if I have time to pull the gas block tonight, but I probably won't. It was pretty snug to put on. And it's on an Aero upper. I broke down my 300BLK to steal the upper so I could get this project going.

Not the best pic, but here it is. I'll post more tonight.
8aed4f1ffec11d384e1bc8c57abace82.jpg

[steyrman13]

Check out my thread here. HELP Weird Cycling Issues 10.5"
https://www.m4carbine.net/showthread.php?t=179357
Yours sounds similar symptoms that I was working on with that upper.
In short
The gas port alignment was fine, BCG worked I other uppers, his lower worked fine with other uppers, the only issue was for sure his upper (barrel gas port, tube or gas block) it came down to the barrel gas port measured correctly, but the gas block fitment was slightly loose( could easily slide it over the barrel with no resistance) so gas was leaking between the gas block and barrel and also leaking around the gas tube where it met the gas block. It was enough gas bleed off to cause short stroking issues like you are seeing. I had to try several gas blocks and tubes to get one that didn't leak.

[The FNG]

Check out my thread here. HELP Weird Cycling Issues 10.5"
https://www.m4carbine.net/showthread.php?t=179357
Yours sounds similar symptoms that I was working on with that upper.
In short
The gas port alignment was fine, BCG worked I other uppers, his lower worked fine with other uppers, the only issue was for sure his upper (barrel gas port, tube or gas block) it came down to the barrel gas port measured correctly, but the gas block fitment was slightly loose( could easily slide it over the barrel with no resistance) so gas was leaking between the gas block and barrel and also leaking around the gas tube where it met the gas block. It was enough gas bleed off to cause short stroking issues like you are seeing. I had to try several gas blocks and tubes to get one that didn't leak.

This is what I'm betting on, but I'll dig a little deeper still and see what the issue could be. Thanks.

[BufordTJustice]

Yes, I've tried 2 Pmags and 2 Noveske GI mags.



I'm not sure I'm getting any gas leakage from the barrel/ block mating area, but there is some on from the tube. It does not seem excessive, but I can post pictures when I get home tonight. I will pull my BCG apart tonight and inspect along with pictures. It is a carrier I bought from IG, so I don't know the brand, but I would assume it to be quality because it came from him. The bolt is a PSA (I know) but my Noveske BCG was stolen about a month ago when my truck was broken into, so its all I have right now until my new carriers come in (I bought two more from IG and I have 2 bolts I bought from Noveske). I will see if I have time to pull the gas block tonight, but I probably won't. It was pretty snug to put on. And it's on an Aero upper. I broke down my 300BLK to steal the upper so I could get this project going.

Not the best pic, but here it is. I'll post more tonight.
8aed4f1ffec11d384e1bc8c57abace82.jpg

Well, if you bought the carrier from IG, it's gonna be good to go. Worth checking the bolt gas rings though. I agree with Clint and IG that is seems to be a gas drive issue. I suspect Steyrman may be on the right track. I know Clint offers gas blocks with a slightly tight interior dimension at Black River Tactical for situations like this.

My SLR Sentry 6 Ti set screw fit nice and tight on my Gunner 18", for what that' worth. But, you honestly don't need an adjustable gas block for your uses unless you plan to suppress your upper...it would be a waste of money for you.

Aero upper should be fine and dimensionally in-spec.

So, you bought the gas tube and gas block from Faxon?

[The FNG]

Ya the tube, block, and barrel are Faxon.


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[The FNG]

Sorry guys, I didn't get a chance to look deeper. My wife already packaged it up to be sent to Faxon. I'll update the thread when I hear from them.


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[Clint]

The 18" rifle can be a little more sensitive to gas leaks, gas port size and buffer weight than some other configurations, but will work great if properly sized and assembled with quality components.

[TomMcC]

I have a Faxon 18" Gunner. When new and with a new bolt I experienced occasional short stroking. My fix was to manually rack the BCG about 1000 times, yes a 1000, over about a week. I also made sure everything was well lubed. Works fine now. Hope this helps.

Also, I'm running a rifle buffer.