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  1. #1
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    13.7" build. Need help troubleshooting please!

    Hi all,
    I am REALLY hoping y'all can help me figure my issue out..... I have built a 13.7" midlength build (specs that matter will be below). The weapon shoots like a dream, but it is only functioning off XM193 and M855 ammo. This would be primarily what I feed it anyway, but the fact its not consistent or so picky has be strongly believing I have a gas problem. I can run those rounds ok but I tried some SS109 and steel case that was in my bag and both failed. I have a lot of money invested in this build and this makes me so sad. Im sure I must have done something wrong, but I dont know what or if something is defective.

    1. If I swap the BCG, the issue seems to remain
    2. If I swap the entire upper, the issue seems to go away

    This is bothering me so much, that I compiled a video showing ejection patterns and the issues- https://youtu.be/TTgF_UFnxus

    Build Specs:
    13.7" Sons of Liberty Gun Works barrel (.750')
    Sons of Liberty Gun Works Lo Profile gas block (.750")
    Spikes Tactical midlength gas tube
    BCM BCG
    Vltor A5 complete buffer system (A5 receiver extension tube, green springco spring, A5 H2 Buffer 5.3oz)
    Aero upper receiver


    Thanks for any help you all can offer me in this frustrating time!

  2. #2
    MGO Member
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    You need to start with a test to see if it is cycling fully. Load one of the questionable rounds in a mag a fire it and see if it locks open on en empty mag. If it does you don't have a gas problem. If it doesn't then you're not getting enough gas pressure to function properly. Try several rounds just to make sure it's repeatable. Do that function test and report back and then we will know where to go from there to troubleshoot.

  3. #3
    MGO Member Imshootin's Avatar
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    Quick search I did has a lot of discussion regarding gas port size and buffer weight.

    Throw the below into Google's search and you'll find lots to peruse and chew on.

    issues 13.7 inch barrel mid gas system
    If you are better off than you were 4 years ago....................you are probably an ILLEGAL INVADER.

  4. #4
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    Quote Originally Posted by Jailer View Post
    You need to start with a test to see if it is cycling fully. Load one of the questionable rounds in a mag a fire it and see if it locks open on en empty mag. If it does you don't have a gas problem. If it doesn't then you're not getting enough gas pressure to function properly. Try several rounds just to make sure it's repeatable. Do that function test and report back and then we will know where to go from there to troubleshoot.
    sorry, I forgot to add this.... I did test that as well. It does not lock back. Seems bolt doesnt have enough pressure to get all the way behind round on last round or any round to strip and chamber on lower pressure ammo.

  5. #5
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    Quote Originally Posted by Imshootin View Post
    Quick search I did has a lot of discussion regarding gas port size and buffer weight.

    Throw the below into Google's search and you'll find lots to peruse and chew on.

    issues 13.7 inch barrel mid gas system
    not disagreeing with you, but the buffer system, barrel, gasblock etc are an exact match to what sons of liberty puts in their factory 13.7 builds.. (what im cloning)

  6. #6
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    OK lots of things to check when you have a gas issue. Check the gas key for proper staking and signs of leakage. Check the gas tube to make sure there are no obstructions. Check the gas rings on the bolt to make sure you don't have broken rings. Check gas block alignment to make sure the gas port isn't partially covered by the gas block. Check the gas block itself to make sure the gas is passing freely. If all those things check out the last thing to check is the gas port itself to make sure it's to spec. If everything checks out you may have to open up the gas port on the barrel to allow more gas to function the BCG.

  7. #7
    MGO Member Imshootin's Avatar
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    Quote Originally Posted by darkwang View Post
    not disagreeing with you, but the buffer system, barrel, gasblock etc are an exact match to what sons of liberty puts in their factory 13.7 builds.. (what im cloning)
    I just stated a couple possibilities from info that came up from a search and suggested you do the same. Have you bothered calling them since it's all their parts? You might want to find out what size the gas port in the barrel is supposed to be and check to make sure a drilling step wasn't missed and it's undersized. You obviously are lacking the gas pressure needed to properly move the mass that needs moved.
    Good luck.
    If you are better off than you were 4 years ago....................you are probably an ILLEGAL INVADER.

  8. #8
    MGO Member Moleman-'s Avatar
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    I'd do everything Jailer suggested especially go through and verify the gas tube to block alignment as well as the block to port alignment. What is your gas port size? Have you tried the setup with a lighter H or even standard buffer? I had the same thought about the midlength gas system on a 13.7" barrel. Just because they sell it doesn't mean it will function ideally and not be finichy.

  9. #9
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    thank you. I guess I could give that a shot! i kind of figured since it is still a "franken gun" I might not be able to call them the same. Ill get the port size measured and verify against their spec.

  10. #10
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    Im not sure if I can put a standard buffer in with the Vltor rifle length spring and tube? I guess it would work in theory? Gas block seems aligned fine. It was a dimpled barrel and I can tell the set screw is deeper meaning its in the dimple. I guess I need to check tube to block alignment. Is there a way to actually mess that up since its pinned? SOLGW spec for that barrel port is .0785"

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