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Posted: 7/10/2014 1:30:49 PM EDT
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I recently had a rifle of mine cerakoted out of state. I just took it out yesterday, and for the first time ever in over 1k rounds I had some FTE/ double feeds. This rifle has been exceptionally smooth, in the previous range sessions, before the cerakoting.
The only possible thing I can think of is the gas block placement. I'm not sure exactly where it was before as the rifle was built by a professional rifle builder, and never malfunctioned, but when comparing it to my other rifles gas blocks it appears to be set almost a milimeter from the raised area(flange?)on the barrel where the gas block is supposed to meet I assume. Only other issue is this is my only, clamp, lo pro gas block. The others are all set screw ones,so I'm not sure if placement differs. Could such an offset of a MM or less cause these sort of issues for my gun? The entire rifle is coated including barrel and gas block, I assume the rifle was assembled then coated. Is this going to be a problem to fix. Eta. I already tried to remove it and place it further back. The gas block is so thight I bent the only 2 Allen keys I have that fit it. 
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The barrels I have worked with have a gas port drilled with the assumption that there will be a usgi end cap between the gas block and that shoulder. I measure, but even low pro gas blocks usually need to be off the shoulder a bit. I assume you aren't using usgi hand guards?
Sounds more like a cleanliness problem. What ammo? is the extractor ok? Eta: fixed a word and added a thought. |
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Few questions and a tip
Tip: those screws are going to be locktite for the most part so hit it with a torch and they should move Question 1:) is the inside of the upper cerakoted? If yes do you feel any roughness when you charge it? 2:) did you have the barrel cerakoted? 3:) did you change out any springs or clean the extractor lately? 4:) was your barrel designed to have the spacer between the gas block and shoulder of the barrel? 5:) did you give everything a good soak in oil? |
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Quoted:
The barrels I have worked with have a gas port drilled with the assumption that there will be a usgi end cap between the gas block and that shoulder. I measure, but even low pro gas blocks usually need to be off the shoulder a bit. I assume you aren't using usgi hand guards? Sounds more like a cleanliness problem. What ammo? is the extractor ok? Eta: fixed a word and added a thought. Same ammo I've always used, PMC bronze. I've run thousounds of rounds through some of my ars and have never had to clean a gas tube, what could I clean? Rifle got a clean right after she was returned home. |
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Quoted:
Few questions and a tip Tip: those screws are going to be locktite for the most part so hit it with a torch and they should move Question 1:) is the inside of the upper cerakoted? If yes do you feel any roughness when you charge it? 2:) did you have the barrel cerakoted? 3:) did you change out any springs or clean the extractor lately? 4:) was your barrel designed to have the spacer between the gas block and shoulder of the barrel? 5:) did you give everything a good soak in oil? 1 yes. A tad bit actually, definitely rougher then a standard anodized upper. 2 yes, it appears he assembled the barrel gas block/tube, then sprayed. 3 no, but yes it was cleaned well. 4 I don't think so. None of my other rifles have a spacer 5 some oil, lots of grease!
eta. Charging feels pretty smooth...but if I run my finger along it, it's much rougher then a stock mil spec finish. |
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This is why cosmetic add ons are so dumb. They cost money, and can detract from functionality. Chances are you need to shoot a few hundred rounds of full powered 5.56 ammo (NOT PMC Bronze) to mate the surfaces together again after the coating. There is probably extra friction somewhere. And no, 1mm of space between the barrel shoulder and gas block will not make a difference. The gas block port is much larger than the barrel port to account for some mis-alignment. Additionally, as another poster stated, many gas blocks account for a handguard cap between the block and the shoulder.
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Quoted:
This is why cosmetic add ons are so dumb. They cost money, and can detract from functionality. Chances are you need to shoot a few hundred rounds of full powered 5.56 ammo (NOT PMC Bronze) to mate the surfaces together again after the coating. There is probably extra friction somewhere. And no, 1mm of space between the barrel shoulder and gas block will not make a difference. The gas block port is much larger than the barrel port to account for some mis-alignment. Additionally, as another poster stated, many gas blocks account for a handguard cap between the block and the shoulder. I concur. Dump some oil in it, then shoot the crap out of it with some 5.56. |
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Quoted:
1 yes. A tad bit actually, definitely rougher then a standard anodized upper. 2 yes, it appears he assembled the barrel gas block/tube, then sprayed. 3 no, but yes it was cleaned well. 4 I don't think so. None of my other rifles have a spacer 5 some oil, lots of grease!
eta. Charging feels pretty smooth...but if I run my finger along it, it's much rougher then a stock mil spec finish. Quoted:
Quoted:
Few questions and a tip Tip: those screws are going to be locktite for the most part so hit it with a torch and they should move Question 1:) is the inside of the upper cerakoted? If yes do you feel any roughness when you charge it? 2:) did you have the barrel cerakoted? 3:) did you change out any springs or clean the extractor lately? 4:) was your barrel designed to have the spacer between the gas block and shoulder of the barrel? 5:) did you give everything a good soak in oil? 1 yes. A tad bit actually, definitely rougher then a standard anodized upper. 2 yes, it appears he assembled the barrel gas block/tube, then sprayed. 3 no, but yes it was cleaned well. 4 I don't think so. None of my other rifles have a spacer 5 some oil, lots of grease!
eta. Charging feels pretty smooth...but if I run my finger along it, it's much rougher then a stock mil spec finish. Gotcha. Real quick for number two do you mean he built everything and then sprayed it? Everything should be completely dissasembled for cerakoting. If it isn't cycling as smooth as before you may try manually charge it a bunch to break things back in and smooth out any roughness. I would check my extractor and make sure that youre getting some good resistance from the spring. If not a spring change on an extractor or possibly an o ring can really up the extracting power. Cerakote is mean to be applied at .001 thickness but many applicators apply it much thicker and it can cause some tolerance issues. (Again cycling the bolt can help) For oiling after checking your spring, I would oil the bolt through the oil ports in the BCG with a good oil and see if it helps. ETA also check your gas rings. And make sure it is doing it with a couple magazines. Sometimes double feed issues are caused by shoddy followers or worn springs in your magazines. |
| Probably not your gas block, most of them end up being spaced of the barrel shoulder some to achieve proper gas port alignment. I'd be more concerned if it was sitting up against the shoulder. Is your bolt locking to the rear after the last round? If so your gas system is probably fine. FTE / double feeds are often caused by a weak extractor spring allowing the extractor to jump of the rim of the cartridge. Or a worn / damaged extractor. Check to see if your extractor has the black o-ring around the spring. If not try adding one. |
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