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Thread: Cutting a 7.62x39 ar barrel

  1. #1
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    Cutting a 7.62x39 ar barrel

    I have an upper I built with a faxon 16 inch mid gas 7.62x39 barrel. It's been 100% reliable from the 1,500 rounds I put through it, suppressed & unsuppressed. I would like to cut it down to 13.9 & pin/weld. My question is with the 7.62x39 round is cutting the barrel going to give me the same results as cutting a .556 barrel? Meaning softer recoil impulse & less gas in the face while suppressed & maintain reliability. Don't want to risk making it unreliable while the cans not on, but do want it as short as possible & the 13.9 - 14.5 .556 uppers I have are my favorite blasters. Thanks
    Last edited by greene; 11-14-20 at 18:53.

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    I cannot answer your question, but I have learned (from trying and failing to make a piston system work on a mid-gas 18" 7.62x39 barrel) that 7.62x39 develops lower pressure than .556

    The question is whether or not the cut down barrel will have enough dwell time to reliably cycle the action. I don't have the answer, but hopefully someone out there has tried it

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    For what it is worth, my KAK barreled 11" 7.62x39 pistol runs great with no problems cycling.

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    Quote Originally Posted by Pressingonward View Post
    I cannot answer your question, but I have learned (from trying and failing to make a piston system work on a mid-gas 18" 7.62x39 barrel) that 7.62x39 develops lower pressure than .556

    The question is whether or not the cut down barrel will have enough dwell time to reliably cycle the action. I don't have the answer, but hopefully someone out there has tried it
    I have a 2 Faxon 16" mid-gas barrels, both of which I cut down to 14.5" and P&W'd. One of the 2 is normal DI, and that one worked fine as is, didn't need to enlarge the gas port at all. un-suppressed only (I live in a Dem nazi state, fookers). Running Precision Armament M4-72 muzzle brakes on both.

    The 2nd of the 2 is an Adams Arms piston conversion, and I had to enlarge the gas port yuugely, and I would not recommend a piston 14.5 mid-gas 7.62x39. If you're going piston on 14.5" 7.62x39 AR-15, it should be carbine gas.

    yes, I do love my 14.5" P&W'd AR's: 9mm, 5.56, 7.62x39, and AR-10 308.





    Last edited by rpoL98; 11-22-20 at 16:37.

  5. #5
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    Had an 8.5” barrel with faux Pig device for a short while. Bizarrely reliable, but kicked like a 12 gauge. My working assumption was overgassing/back pressure was working based on the slightly exaggerated recoil. I was using a standard spring/ carbine buffer IIRC, but had I kept the upper around, likely would have tried to adjust the recoil impulse with an H2 and different springs.

    If you don’t mind, would love for you to post up your finished project. I have been thinking about doing something similar ~12.5” and suppressed, so very interested in what your experience and outcomes are.

  6. #6
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    What is the gas port size on that 16 inch barrel?
    You are a genuine toolbag if you have your EDC "loadout" in your signature line...

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    Quote Originally Posted by Magsz View Post
    What is the gas port size on that 16 inch barrel?
    Read somewhere it's at .091

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    Quote Originally Posted by Magsz View Post
    What is the gas port size on that 16 inch barrel?
    Faxon 16" 7.62x39 barrels I purchased in 2016, IIRC, gas port was 0.089".

  9. #9
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    Quote Originally Posted by rpoL98 View Post
    Faxon 16" 7.62x39 barrels I purchased in 2016, IIRC, gas port was 0.089".
    Roger.

    If i recall correctly and I will have to verify this, my 10.5 inch gun had a .085 sized gas port and would not run. I enlarged it to I believe .095 and it runs EVERYTHING...really freaking well.
    You are a genuine toolbag if you have your EDC "loadout" in your signature line...

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    Took it out today, ran it with a sprinco blue spring & h3 buffer. Ran great. Locked back on last round. I'm thinking it will have plenty of gas drive still if I cut it down. I'm just not sure if the gunner barrel profile has enough girth where I would cut it to support the 5/8×24 thread pitch

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