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Thread: 9mm AR carbine issues, looking for help

  1. #1
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    9mm AR carbine issues, looking for help

    I have built a 9mm pistol, which I'm waiting on the stamp to come back to SBR. I have a New Frontier Glock mag lower, standard upper, 5.5" barrel, 9mm United Defense Lab bolt (with added weight from factory), carbine/pistol tube with standard carbine spring. I made my own heavy buffer out of cold rolled steel for the extra weight. The buffer is longer than standard, it will clear the mag no problem but is too long to get behind the bolt hold open lever. That is by design, not a mistake on my part. I have no LRBHO on this set up and wanted to minimize the speed of the bolt. I also planned on it being very heavy so that the action would stay closed longer because I will be adding a suppressor 100% of the time. Total weight bolt and buffer is 23.2oz.

    in the build configuration I have, I test fired and when I hold it at arms length I get good function out of a standard G17 mag. When I simulate holding as if it were a carbine it fires but fails to return to battery, in fact the buffer hangs up in the tube, then will move forward again and strip a round. Cases are ejected at 3 o'clock, about 2-3 feet from where I stand. This was with Winchester 147gr FMJ.

    Again, I want as heavy as I can to keep is closed longer for more quiet when suppressed, but it has to be reliable.

    Open to suggestions on what to tweak.

  2. #2
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    Is this function test with a can or without? I didnít follow.

    I am asking my builder about my Atheris 9 mm AR Pistol regarding buffer and spring weight.

    The dynamics of a suppressed gun I have found is using lighter spring weights for reliable cycling.

    I havenít had any issues with my suppressed 9 mm AR Pistol.

    Iíll get back to you with specifics when he responds.


    Sent from my iPhone using Tapatalk Pro

  3. #3
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    Quote Originally Posted by CDR_Glock View Post
    Is this function test with a can or without? I didnít follow.

    I am asking my builder about my Atheris 9 mm AR Pistol regarding buffer and spring weight.

    The dynamics of a suppressed gun I have found is using lighter spring weights for reliable cycling.

    I havenít had any issues with my suppressed 9 mm AR Pistol.

    Iíll get back to you with specifics when he responds.


    Sent from my iPhone using Tapatalk Pro
    Testing without a can. Just a 5.5" barrel.

  4. #4
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    My builder used a 7-8 oz buffer for my 9 mm build.

    If itís not cycling without a can, there is likely an issue with your buffer spring.

    Mine shoots suppressed without issues, using 147 or 158 gr 9 mm subsonic ammunition.


    Sent from my iPhone using Tapatalk Pro

  5. #5
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    Quote Originally Posted by CDR_Glock View Post
    My builder used a 7-8 oz buffer for my 9 mm build.

    If it’s not cycling without a can, there is likely an issue with your buffer spring.

    Mine shoots suppressed without issues, using 147 or 158 gr 9 mm subsonic ammunition.


    Sent from my iPhone using Tapatalk Pro
    I'm going to admit my mistake, and it was stupid.

    I never tightened down the castle nut on the buffer tube. Apparently the tube being loose had enough flex that when any pressure was put on it, the buffer would be put in a small bind and hang up.

    I actually did put the buffer back in the lathe and cleaned up the end that mates to the bolt carrier just to make sure. I also gave it just a slight chamfer so it would slide well. That brought the weight down less than half an ounce.

    So boys and girls, I know you get excited to try out that new build, but make sure everything is tight.

  6. #6
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    Quote Originally Posted by mr fixit View Post
    I'm going to admit my mistake, and it was stupid.

    I never tightened down the castle nut on the buffer tube. Apparently the tube being loose had enough flex that when any pressure was put on it, the buffer would be put in a small bind and hang up.

    I actually did put the buffer back in the lathe and cleaned up the end that mates to the bolt carrier just to make sure. I also gave it just a slight chamfer so it would slide well. That brought the weight down less than half an ounce.

    So boys and girls, I know you get excited to try out that new build, but make sure everything is tight.
    Absolutely.

    Best of luck. Shooting suppressed is so fun.


    Sent from my iPhone using Tapatalk Pro

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