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Thread: Gas Block

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    GuncoHolic BBill's Avatar
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    Default Gas Block

    Does anyone know what the diameter of the gas block hole in the barrel is for a 7.62x39 ar-15 is? Its a Model 1 ER Shaw 20in barrel. I've got the dented primers solved-now sometimes it short strokes.Think I might have to open it up a little. All kinds of ammo, not just russki. Someone on ar-15.com said a #44 drill was the correct size but I don't want to screw the barrel up. Thanks, Bill

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    Gunco Addicted for life j427x's Avatar
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    most are .750 on the h-bars.

    i can't recall what my gas port was on the del-ton--but i only enlarged it by one step and that solved the problem. unfortunatly i can't recall what size bit i used out of a bit box with 300 bits in it. being that your barrel is a 20" my sized port would likely be wrong as 16" and 20" ain't the same on the port.


    the only barrels in 7.62x39 i have seen so far that wern't right on the edge of a too small port has been the m4 profile citadel-- which seems to run out of the box on about anything.

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    GuncoHolic BBill's Avatar
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    OK- Thanks, I'll go one bigger and try it tomorrow. I'll let you know-Bill

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    GuncoHolic BBill's Avatar
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    Hey 427- You meant .075 didn't you? I bought some numbered drill bits and a #44 is 0860.That would be a little bit larger. I'll chuck it up and go for it! The only numbered drill I had before this were #40 #42Aircraft and #3 drills from CNC Gunsmithing for 80% recievers.

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    Gunco Addicted for life j427x's Avatar
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    Post1911

    Quote Originally Posted by BBill View Post
    Hey 427- You meant .075 didn't you? I bought some numbered drill bits and a #44 is 0860.That would be a little bit larger. I'll chuck it up and go for it! The only numbered drill I had before this were #40 #42Aircraft and #3 drills from CNC Gunsmithing for 80% recievers.

    don't drill anything yet!-- 750 of an inch on the barrel diameter! for the gas block to fit the barrel --err not the port size.

    i don't know what size to use on the port --although .075 might work--i'll search around the net--there has got to be some info some where on a 20" 7.62x39 port size--

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    Gunco Addicted for life j427x's Avatar
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    OK here is the best info i can find on the 20" 7.62x39 gas ports--

    .97 through to .125 -- yea i know .125 sounds like an awful lot --but there is a big pressure drop on a 20" gas system and the 7.62x39 is a very low pressure round to start with. another guy says drill bit size 28 through 30

    now this info is just internet stuff-- i haven't tried these sized ports on a barrel. it is logical though that a 20" would need a big port in a 7.62x39 though.

    you might try these first-- lighter buffer spring? a light buffer?

    i think on the 7.62x39s many people are just copying what works for a 5.56 and the 7.62x39 requires a totally new sized port and port map generally speaking.

    good luck with the 7.62x39 project!

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    bowman bowman's Avatar
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    Quote Originally Posted by BBill View Post
    Does anyone know what the diameter of the gas block hole in the barrel is for a 7.62x39 ar-15 is? Its a Model 1 ER Shaw 20in barrel. I've got the dented primers solved-now sometimes it short strokes.Think I might have to open it up a little. All kinds of ammo, not just russki. Someone on ar-15.com said a #44 drill was the correct size but I don't want to screw the barrel up. Thanks, Bill
    bill
    frist check the diameter of your gas vent.then clean your bolt. ar,s dump gas directley into the bolt to cycle.if its carboned up this will cause a short cycle.if all is good only open up the vent hole .010 at a time untill you get the cycle rate you want.

    bowman

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    GuncoHolic BBill's Avatar
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    Used a 9/64 drill and out of two mags of 20 each only had one short stroke. Might go one size bigger and be done with it. Hey j4- I trimmed the front of my firing pin a few thou and the inside of the back and NOT ONE dented primer!

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    GuncoHolic BBill's Avatar
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    Quote Originally Posted by bowman View Post
    bill
    frist check the diameter of your gas vent.then clean your bolt. ar,s dump gas directley into the bolt to cycle.if its carboned up this will cause a short cycle.if all is good only open up the vent hole .010 at a time untill you get the cycle rate you want.

    bowman
    I'm a clean freak- Every thing gets cleaned after firing. All I use is CLP and SLP2000. Gotta run em wet!!

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    Gunco Addicted for life j427x's Avatar
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    Post1911

    i figured you would get the 20" tuned up!




    Quote Originally Posted by BBill View Post
    Used a 9/64 drill and out of two mags of 20 each only had one short stroke. Might go one size bigger and be done with it. Hey j4- I trimmed the front of my firing pin a few thou and the inside of the back and NOT ONE dented primer!

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