AR15 firing issue

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  • RayHerkes

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    Aug 18, 2019
    3
    1
    Mandeville
    I have a 7.62x39 AR Upper on a Spikes lower with PSA parts kit. The firing pin strikes the primer but round does not fire. I know it’s something in the lower part of the rifle because I can switch it out with my smith and it works fine. Any recommendations on what it can be or someone to take it to?

    Thanks
     

    Tboy

    Moving forward
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    Jul 14, 2008
    1,636
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    Greenwell Springs
    Are you switching out uppers to the smith lower and it works? Or the non functioning lower to the smith upper?

    A pic of the inside of the lower might be useful.
     

    dougstump

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    Nov 22, 2010
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    If you are in the Shreveport area I'll be happy look at it for you. At a guess, I'd suspect that the hammer spring is installed wrong.
     

    Bigchillin83

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    Feb 27, 2012
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    Livingston
    Is hammer spring tips sitting on trigger pin or under trigger pin? Needs to be on top of trigger pin. Or hammer spring installed backwards or needs a higher power spring for the harder 762 primmers
     

    shrxfn

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    Oct 25, 2015
    855
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    SWLA
    If I remember right the 7.62x39 takes a little longer firing pin than the normal 5.56 one. I did a Google on it and it should be .010 longer. From the forum posts, I read sometimes the shoulder of the pin is machine farther back so the firing pin is the same length but it will be longer from the shoulder to the tip of the pin.

    Did you put a 5.56 firing pin in it or the 7.62?
     

    jtj5002

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    Feb 7, 2016
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    Lacombe
    You need a proper firing pin/bolt combo for 7.62x39. Either a standard 7.62x39 bolt with an extended firing pin, or a 7.62x39 bolt with shortened tail and a standard firing pin.
    Assuming your FCG in your lower is installed properly, it could just mean your Smith have just a slightly stronger hammer spring. Properly setup 7.62x39 upper should reliably ignite with any lowers.
     

    RayHerkes

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    Aug 18, 2019
    3
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    Mandeville
    Are you switching out uppers to the smith lower and it works? Or the non functioning lower to the smith upper?

    A pic of the inside of the lower might be useful.
    I can get a pic but it will be a few days. I Put the AK upper on the Smith lower and it works.
     

    MTx11B

    Combat Vet
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    Aug 31, 2013
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    NOLA
    There are a handful of things you can do to narrow it down to issue, by chance did you swap fcg or even just hammer and spring between lowers? 7.62x39 ammo is notoriously hard primed as others mentioned, could be just a low powered spring with AR hammer springs we always have the option of giving the hammer spring an extra winding when installing just to be sure that is the issue before spending more money on parts and delving into the "maybe realm"

    Sent from my SM-N960U using Tapatalk
     

    georg jetson

    Well-Known Member
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    Apr 19, 2012
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    As mentioned already, standard AR hammer springs are not strong enough to reliably fire Russian surplus ammo. Do you have the same problem with commercial ammo?

    Wolf makes a heavy hammer spring that has made my 7.62x39 upper fire reliably. However, keep in mind the mechanics of the standard AR trigger. A heavy hammer spring will increase your trigger pull considerably. I bought an adjustable trigger to bring my trigger pull down to 3lbs.
     

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