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Thread: Strange Issues - BCM even baffled

  1. #1
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    Strange Issues - BCM even baffled

    Been communicating back and forth with BCM the last couple days and even they are baffled.

    Setup

    BCM Blem Upper
    BCM 14.5in Midlength barrel
    BCM Mod 1 Comp
    BCM BCG
    BCM lo-pro gas block
    BCM gas tube
    Geissele SMR MK2 13in

    BCM complete lower
    BCM H buffer
    BCM carbine spring


    Problems -

    Bolt Over Ride
    "Partial Loading" - no double feeding but not completely loading the next round.

    Its definitely a gas issue as it progressively gets worse. Today it is now a "bolt action" rifle as all it does is bolt over ride the fresh round.

    It is extracting just fine but is not feeding the next round.

    Yesterday I could get exactly 3 rounds off before it would either over ride or partial load the next round and jam.

    Yes, I've tried 3 different BCM BCG's, 8 different magazines, 5 different types of ammo. All of the parts I swapped out work flawlessly on the 3 other rifles I use them in(11.5in BCM SBR, 16in BCM RECCE, 18in BCM 3gun Rifle).

    That's what has all of us baffled. The fact I've tried so many different parts, mags and ammo(no handloads, only factory ammo including NATO pressure ammo).

    Here is a picture of the "partial load" I'm taking about. There is not a round in the chamber.


  2. #2
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    Have you tried the upper on a different lower. Or different buffers?

  3. #3
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    You need to put the entire upper on to another lower and try it. I would also change the gas tube. I remember markm had an upper where the tube was worn near the lip where it meets the key and it was causing a progressive short stroking scenario.



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    JW, did you leave a gap between the gas block and the shoulder on the barrel?

  5. #5
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    Quote Originally Posted by steyrman13 View Post
    Have you tried the upper on a different lower. Or different buffers?
    Steyrman and IraqGunz -
    Have tried different lowers(that had different buffers)

    Just tried replacing the gas tube. It seemed to fix some of the problems. Now the NATO pressure stuff cycles fine but does not lock back on empty(4 different mags used to test) but the weaker 223 stuff, which I don't expect much from to begin with, still makes it a bolt action.

    MT Dawg -
    Barrel is dimpled, when you tighten the screw down into the dimple it self centers and leaves a gap.

    Seems the gas tube was part of the problem. I can't even run water through it.....

    Gas port is at .077, which seems slightly under sized. I think I read on here some where that 14.5 Mid gas ports are usually .080-.085?

  6. #6
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    jw,

    The port size should be around .078 so you are good. I suspect that since we now know the tube was an issue you had a perfect storm of gas issues. See if you can locate a gas block that is tighter in the barrel.

    Does the gas block fit tightly or is it easy to slide on?

    Quote Originally Posted by jwfuhrman View Post
    Steyrman and IraqGunz -
    Have tried different lowers(that had different buffers)

    Just tried replacing the gas tube. It seemed to fix some of the problems. Now the NATO pressure stuff cycles fine but does not lock back on empty(4 different mags used to test) but the weaker 223 stuff, which I don't expect much from to begin with, still makes it a bolt action.

    MT Dawg -
    Barrel is dimpled, when you tighten the screw down into the dimple it self centers and leaves a gap.

    Seems the gas tube was part of the problem. I can't even run water through it.....

    Gas port is at .077, which seems slightly under sized. I think I read on here some where that 14.5 Mid gas ports are usually .080-.085?



    Owner/Instructor at Semper Paratus Arms

    Facebook: https://www.facebook.com/SemperParatusArms/

    Semper Paratus Arms AR15 Armorer Course http://www.semperparatusarms.com/cou...-registration/

    M4C Misc. Training and Course Announcements- http://www.m4carbine.net/forumdisplay.php?f=141

    Master Armorer/R&D at SIONICS Weapon Systems- http://sionicsweaponsystems.com

  7. #7
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    Quote Originally Posted by jwfuhrman View Post
    Steyrman and IraqGunz -
    Have tried different lowers(that had different buffers)

    Just tried replacing the gas tube. It seemed to fix some of the problems. Now the NATO pressure stuff cycles fine but does not lock back on empty(4 different mags used to test) but the weaker 223 stuff, which I don't expect much from to begin with, still makes it a bolt action.

    MT Dawg -
    Barrel is dimpled, when you tighten the screw down into the dimple it self centers and leaves a gap.

    Seems the gas tube was part of the problem. I can't even run water through it.....

    Gas port is at .077, which seems slightly under sized. I think I read on here some where that 14.5 Mid gas ports are usually .080-.085?
    I'm wondering if the gas port is properly aligned with the block. Think the dimple itself might be a little off?
    "People have always been stupid. The Internet just makes it easier for us to know about them." - donlapalma

  8. #8
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    Obstruction in the carrier key or loose carrier key?

    You might want to pull the gas block and check the little ring o' carbon around the gas port. It will tell you right off if the gas block is aligned to a reasonable degree...

  9. #9
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    Quote Originally Posted by Iraqgunz View Post
    jw,

    The port size should be around .078 so you are good. I suspect that since we now know the tube was an issue you had a perfect storm of gas issues. See if you can locate a gas block that is tighter in the barrel.

    Does the gas block fit tightly or is it easy to slide on?

    It fits tightly, doesn't slide on and off very easily. The weaker ammo like wolf and some federal 55gr frangible I'd like to use as a I have a ton of the wolf 55gr I got for the short range stages at 3gun's and for running drills so I don't have to worry about my brass. The frangible I like because we can run drills with steel targets really close and not have any thing coming back after us.

    I'm going to order a different gas block and give it a try.

  10. #10
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    Quote Originally Posted by MK18Pilot View Post
    Obstruction in the carrier key or loose carrier key?
    He tried 3 different BCGs so not that.

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