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Too much headspace on new AR15 build

Discussion in 'Build it Yourself' started by insomniac, Sep 6, 2019.

  1. mac1911

    mac1911 NES Member

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    Also loctite dies not like to cure on coated metals like park or any othet type of coating. This is why loctite has a primer
     
  2. Warm_Garand

    Warm_Garand

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    OK.

    Good luck.
     
  3. mac1911

    mac1911 NES Member

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    Any headway on this matter?
     
  4. insomniac

    insomniac NES Member

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    I see what you did there.

    Sooooo.....when I was headspacing, I, uh, may have forgotten to put the bolt cam pin back in. Super obvious in retrospect, because the bolt cam pushes the bolt forward a little. Great Road Firearms showed me and didn't even call me an idiot at the same time, so I'm super grateful.

    I do have a cycling problem. First round fires fine, cycles. Second round fires, and then *click*. I'll find that the bolt is half open and has scraped the side of the next round. I tried it in both .223 and 5.56 for kicks, and this was on a carbine buffer. Looks like I'm gunsmith bound, because I'm missing the tooling to tear it down.
     
  5. richc

    richc NES Member

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    I'm guessing gas tube problem. Are you using the right tube? I've seen that happen.

    Is the gas block installed properly? Is the gas tube protruding far enough to engage?

    There should be plenty of energy available to cycle the action. Sum Ting Wong.
     
  6. jayhitek

    jayhitek NES Member

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    try a heavier buffer. H2
     
  7. KMM696

    KMM696 NES Member

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    Not a high probability problem, but one more thing to check.

    If first one fires, second one jams can be translated as cartridges loading from one side of the magazine work fine and the other side jams and your upper has M4 style feed ramps that extend from the receiver through the barrel extension, check the feed ramps to make sure the feed ramp section of barrel isn't protruding a bit, catching on the bullet tip or edge of the case mouth. It's okay if the feed ramp on the receiver is higher than the barrel ramp, as that just creates a little cliff for the cartridge to fall off of on it's way to the chamber. If the barrel ramp is higher, it's a wall for the cartridge to run into.

    It's 5 minutes work with a dremel and pointed grinding wheel to fix, but you should try to find someone who's done it before.

    this AR15Barrels.com link


    is to a picture that is intended to show the difference between standard and M4 ramps, but it also gives a good idea where to look for misalignment.

    Good luck.....
     
  8. jayhitek

    jayhitek NES Member

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    I disagree, In a situation like this, the first one usually fires fine because the BCG is manually thrown forward when you release it with the button and it picks up a cartridge with all that force behind it.. the 2nd bullet is now relying on the gas and buffer cycle..
    I think asking him to tweak the feed ramps is a drastic step to take right out of gate before swapping a few parts to see if it changes anything..
     
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  9. KMM696

    KMM696 NES Member

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    I'm asking him to check the ramps. If they need work, I told him to find someone who knows what they're doing. It's an accumulated budget build, so he probably doesn't have boxes of spares lying around to start swap-out troubleshooting. Feed ramps he can check with a pencil or a nail or a cocktail straw or.... you know, something he can do with what he's got lying around the house.
     
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  10. mac1911

    mac1911 NES Member

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    Maybe a video of the problem.

    so you get 2 shots off and when feeding 3rd shot it fails to feed and bolt is not closed...?
    Try other magazines.

    What you should do.
    1. Load 1 round in the mag, seat mag cycle charge handle.
    does cartridge chamber if yes go to Fire the one shot , does bolt lock back? If yes go to 2 . If no you have a mechanical issue.
    2. Fire some more single shots- confirm all is well.
    3.load 2 rounds and continue.

    Once you can duplicate the problem you can start to figure it out. Start with a different mag.
     
  11. Comrade Moustache

    Comrade Moustache NES Member

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    Need more data
     
  12. Warm_Garand

    Warm_Garand

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    Let's all be perfectly clear.

    You have a carbine buffer, with a carbine spring, in a carbine buffer tube, correct?

    If so, next stop is gas.

    ETA: Here is an explainer on M4 feed ramps, courtesy of Larue Tactical.

    https://www.everydaymarksman.co/wp-content/uploads/2019/03/feedramp.jpg

    There is really only 1 combination that might cause you problems. Pretty low probability on a 16" barrel.
     
    Last edited: Oct 10, 2019
  13. CrackPot

    CrackPot NES Member

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    I agree. Gas. I recently had a problem where the gas block was out of spec. It’s opening to the barrel was not correctly offset so if pushed fully against the barrel collar it partially blocked gas flow. Offsetting it very slightly from the collar fixed all my problems. I could not replace it easily since I had already pinned the muzzle break.

    not all parts are in spec. Focus on the easy ones first. Gas.
     
  14. mothybee

    mothybee NES Member

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    I assume you tried a different mag first.
     
  15. Warm_Garand

    Warm_Garand

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    Probably best not to assume anything, but (assuming he isn't using a carbine spring and buffer in a rifle-length buffer tube) the problem sounds like short stroking.

    Check gas tube for obstruction.

    Lube the rifle.

    Try a known-good mag.

    Try a different/known-good bolt to rule out leaky gas key.

    Try a heavier buffer (on the off chance that the rifle is so over-gassed that the bolt velocity is too fast to allow the mag to feed). Usually over-gassed feeds just fine, but fails to lock back on an empty mag.
     
  16. Supermoto

    Supermoto NES Member

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    Thats because some gas blocks are designed so that they can be used with a handguard cap. You need to leave a 1/32" gap to the barrel shoulder if you are using a free floating handguard. Easy way to tell on a set screw gas block is to spin it upside down. The gas port is drilled thru the set screw hole, so you can see the alignment and know if you need to offset or not
     
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  17. 1903Collector

    1903Collector NES Member

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    That could have ended badly if you fired it!

    I must be a lucky SOB, I got about 2 dozen builds under my belt, they all worked 100% from the get go or just need a couple mags to loosen things up a bit. Hope you get yours up and running.
     
  18. insomniac

    insomniac NES Member

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    Woo, activity on this thread! Unfortunately I haven't had time to get out to the range to further diagnose, but I figure at this point it's almost certainly the gas system.

    Correct. I did have feed problems on a rifle buffer, spring, and tube as well, but replicated it with carbine buffer, spring, and tube.

    No, but on the rifle buffer, spring, and tube, I was using a different mag. I will try a different mag next time I get out to test fire, but these were brand new ten round magazines so I doubt this is the problem.

    Oh, no, I wasn't trying to fire it with the cam out; I meant when I was headspace checking, I left the cam out.

    I think the vast majority of builds have no issues, I just must have mucked up the gas tube installation or something. Unfortunately I don't have the tools to do a tear down yet.
     
  19. Warm_Garand

    Warm_Garand

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    How far are you from Harvard Sportsmen's club?

    It's going to be raining Saturday in the am, but it shouldn't suck too bad later in the afternoon.

    I'd propose trying a known good mag, bolt, and maybe even an H/H2/H3 buffer on a known good carbine lower.

    Let me know if that might work for you.
     
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  20. CrackPot

    CrackPot NES Member

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    Good advice. I keep a box with 3 different weight buffers, 2 different springs, known good mag and some tools. I also have a "known good carbine" so full upper and full lower both that are in spec and function and have been cross tested with other uppers/lower. I also have a known good rifle. Then when I have a problem child, I take the good rifle or carbine and the box of stuff to the range and isolate. swap in upper and lower to figure out where problem is (upper or lower). Then start changing parts out to figure out the issue. My last issue was the 1/32" offset on the gas block. The time before that it was a gas issue addressed with buffer weight. etc.
     
  21. mac1911

    mac1911 NES Member

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    "Generally" if you have a gas system problem with fail to feed issues its constant.
    I would not mess with the buffer system unless the wrong parts are installed in the wrong tube.
    Your not going to have cycling issues with any "normal" length buffer tube and spring/buffer set up.
    A rifle length gas system will and should function fine with a carbine buffer set up and a carbine gas system on a rifle length buffer set up.
    As for gas system problems , I only been messing with ARs since 2008. What I have seen amongst friends.
    Loose or material stuck in gas key. Loose gas tube= did not pin the tube in gas block. i have come across 2 bad gas ports.
    One in which the hole was not drilled through. The other was drilled off line and the gas block covered about 1\2 the hole.
    Good thing was it was a optics only rifle so we just off set the gas block and drilled a few divots for the set screws in the correct location.
    The highest problem has been mags or grossly out of spec discount parts.
     
  22. Warm_Garand

    Warm_Garand

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    Thanks for the sage advice.

    Why don't you meet up with him?

    And just out of curiosity, how are you going to rule out over-gassed/bolt velocity issues?
     
  23. insomniac

    insomniac NES Member

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    Thanks for the offer, can't do this weekend (out of town). The upper assembly (sans the upper itself, which is just a milspec M4 flat top upper) is from Wyndham Weaponry, so I'd hope it's alright. Maybe I can use this as an excuse to finally buy a bench vise.
     
  24. insomniac

    insomniac NES Member

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    I feel like I'm watching an episode of House, AR-15 edition. Is it the gas system? Is it Lupus? IT'S NOT LUPUS.
     
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  25. Warm_Garand

    Warm_Garand

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    OK.

    Here is a thread from someone with the exact same symptoms.

    I found it googling "Boise Tactical".

    AR 15 not picking up the next round

    His issue turned out to be a mis-aligned gas tube.

    Good luck.

    ETA: My final word of advice in this thread would be this: Don't buy cheap parts. Ever. Buy good parts from known manufacturers on sale. Always.
     
    Last edited: Oct 11, 2019
  26. insomniac

    insomniac NES Member

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    Interesting thread! Good find. The BCG on paper sounds really good. In that thread it appears he had a misaligned gas tube, so that gives me an additional thing to consider. Maybe I'll see if I can borrow a friend's BCG to test later.
     
  27. rep308

    rep308 NES Member

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    Tim Gostling at Gartman Arms has debugged a few AR issues for me. He knows what he is doing.
     
  28. mac1911

    mac1911 NES Member

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    I have offered to meet up, times and distances dont agree
    I personally can not say I have successfully diag or even see Over gassed system that I can say "yup over gassed" . Generally from what I have gathered over the years over gassed system will tend not to pick up or even lock back on last round and have a tendency to damage parts.?
     

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