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Thread: Gas Issues

  1. #1
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    Gas Issues

    I built a custom rifle and I finally got out to shoot it. Here's the build thread:

    https://www.m4carbine.net/showthread.php?t=175348

    I was having issues with the bolt locking back after the last round and failure to feed. I swapped with 3 different BCG's, three mags, and two different lowers. All had the same results with the upper. I tried all the same tactics with a different upper to verify that all parts functioned correctly.

    Would I be correct to assume that the gas block is the culprit?


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    Last edited by The FNG; 11-21-15 at 22:38.
    It's better to be thought a fool than to open your mouth and remove all doubt.

  2. #2
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    Your link is broken.

    Tell me more about the magazines. Were all three the same manufacturer?
    Nobody ever got shot climbing over the wall into East Berlin.

    Delivering the most precision possible, at the greatest distance possible, with the highest rate of fire possible.

  3. #3
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    All three were gen 2 Pmags. The bolt catch works with them when operated manually.


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    It's better to be thought a fool than to open your mouth and remove all doubt.

  4. #4
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    Gas Issues?

    Try Pepto-Bismal

    Quote Originally Posted by The FNG View Post
    I built a custom rifle and I finally got out to shoot it. Here's the build thread:

    https://www.m4carbine.net/showthread.php?t=175348

    I was having issues with the bolt locking back after the last round and failure to feed. I swapped with 3 different BCG's, three mags, and two different lowers. All had the same results with the upper. I tried all the same tactics with a different upper to verify that all parts functioned correctly.

    Would I be correct to assume that the gas block is the culprit?


    Sent from my iPhone using Tapatalk
    It could be a misaligned or leaky gas block, leaky gas key, a gas ring problem, an under sized gas port or weak ammo.

    Other possible problems include too much reciprocating mass and/or too much spring rate
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  5. #5
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    Gas Issues

    Since the problem appears to follow the upper, my guess is that it's the gas port and/or leakage with the gas block/tube.
    I know nothing about Faxon but I've seen a lot of their activity here so I'd maybe reach out to them.

    What ammo? I'd try some full power loads too.
    Last edited by Ryno12; 11-22-15 at 00:20.
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  6. #6
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    I'd guess it is a misaligned gas block. Usually gas blocks require a gap between the shoulder of the barrel and the rear of the gas block, and if installed against the shoulder can result in the gas port and gas block orifice not in alignment.

    Secondly, it is a 14.5'' mid length. It probably doesn't need the blue spring, and I would ditch the spikes buffer for a standard H or H2. If the gas block is aligned properly, this would be my second guess.

  7. #7
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    I will try to re-align the gas block to see if that helps. I didn't know it wasn't supposed to sit against the shoulder.

    I really wanted to narrow it down before I contacted Faxon.


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    It's better to be thought a fool than to open your mouth and remove all doubt.

  8. #8
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    Not all gas blocks are made to line up to the gas port with a gap. One gas block I tried was made to fit all the way against the shoulder and I had to shorten it a bit to get it to align with a handguard cap in place
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  9. #9
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    Looks like the question was well answered before I got back to this thread. With magazines being an issue out of the way, it is most definitely an issue of and under gassed - or more concisely an under powered - system.
    Nobody ever got shot climbing over the wall into East Berlin.

    Delivering the most precision possible, at the greatest distance possible, with the highest rate of fire possible.

  10. #10
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    Quote Originally Posted by The FNG View Post
    I will try to re-align the gas block to see if that helps. I didn't know it wasn't supposed to sit against the shoulder.

    I really wanted to narrow it down before I contacted Faxon.


    Sent from my iPhone using Tapatalk
    It's the gas block or tube, like everyone else said. Reinstall that carefully and your problem will go away. Use a new pin if you remove the tube from the block and reinstall.

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