AR trigger troubleshooting

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  • Notalentbum

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    I have a budget AR that I have about 1K rounds through with no issues. To be honest, I don’t recall if this has a trigger I worked on, an aftermarket trigger or the stock budget trigger that came with the lower build kit.
    A few days ago I picked up a 7.62x39 complete upper from Bear Creek Arsenal and swapped it for the 5.56 upper that was on the lower. I took it to Parabellum yesterday afternoon for function and mag testing. Testing didn’t go so great. I had feed issues with the first of my two ASC mags. The rounds weren’t getting their noses onto the feed ramps. Swapped to a C. Products mag and no more feed issues. However I was getting some bump firing if I was sloppy about trapping the trigger back firmly. I played with it for a couple more mags and got it consistently popping off 4-6 rounds at a time. While it’s kinda cool, I’d rather it didn’t do this!!! I’m guessing it is something in the trigger that wasn’t an issue with the lighter 5.56 rounds but has shown to be a big issue with the 7.62. I guess it is also possible that some difference in the BCG could be causing this or a combination of both trigger and BCG.
    Looking for suggestions on what to look for when I tear it down this evening.

    Thanks, Matt
     

    Vigilant

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    Fix it and edit your post, JIC. I’d also not recommended “working” on your trigger if you don’t know what you’re doing.
     

    edwea

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    Not sure it's necessary to get all foil hat about it. Accidental multiples due to equipment malfunction happen. Not often, but they do happen. Asking how to fix seems like a good idea to me.
     

    cb46184

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    Working on a trigger is not rocket surgery. Yes, you need to read and learn everything you can that makes sense, and proceed carefully. The worst that can happen (as long as you handle your firearm safely) is you screw it up and have to buy a few new parts. Then you try again and learn from your mistake. The most important thing my dad every taught me was "If you can't make a mistake, then you can't make anything." The first trigger job I ever did was on my competition AR. I was proud of it after a club member who was a "pro" checked it out and was impressed. You may not do it perfect the first time but, you CAN do it.
     
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    Not sure it's necessary to get all foil hat about it. Accidental multiples due to equipment malfunction happen. Not often, but they do happen. Asking how to fix seems like a good idea to me.

    All that it takes is 1 FUDD to grab his cell phone and make that call. ATF doesn't care if it's a malfunctioning weapon. You may have to try and prove that in court.
     

    Notalentbum

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    No, I pulled the upper off but that is as far as I got. I was hoping someone would chime in and give me some specific issues to look for. I can’t be the only guy this has happened to!

    Matt
     

    55fairlane

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    1) I saw a SKS do THIS......firing pin would stick and slam fire a few times un till worked it's self loose again
    2) possible it's the disconector.....but more then likely.........the round doesn't have enough power to fully push the fire control group back,locking the disconector.....so it slam fires, kicks off a few rounds un till you get either a hotter load or it build momentem and locks the hammer back......

    Hope this helps.....
     

    Hookeye

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    My guess is disconnector spring is missing/damaged or the disconnector itself is damaged.
    I don't think it really slam fires, the hammer doesn't lock back, but has enough delay to not fully follow w the bolt.
    If it rides w the bolt then it would not go boom and need recocked.
    Seen a couple guys with that issue before.

    New springs and or disco fixed em.
     
    Last edited:

    mrproc1

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    Are your trigger pin holes worn out, is the fire control group moving around allowing it not stay in battery after it cycles?
     

    Notalentbum

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    1) I saw a SKS do THIS......firing pin would stick and slam fire a few times un till worked it's self loose again
    2) possible it's the disconector.....but more then likely.........the round doesn't have enough power to fully push the fire control group back,locking the disconector.....so it slam fires, kicks off a few rounds un till you get either a hotter load or it build momentem and locks the hammer back......

    Hope this helps.....


    I don’t believe this to be the case. As long as I fully trap the trigger back it functions perfectly. If I get lazy on the trigger, that is when it fires multiples.

    Matt
     

    JeepHammer

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    Since it fires a few rounds and stops,
    The question is does it stop cock or not?

    If it stops cocked, the disconnect isn't working, and the hammer is catching on the trigger sear.

    A free hammer, hammer not being pushed back far enough to catch disconnect, will always follow the bolt forward and has to be stopped by the trigger sear, which leaves the hammer cocked.

    I imagine what's happening is the 7.62x39 upper has a bolt carrier slightly higher up (in relationship to the hammer) and not fully pushing down the hammer,
    OR,
    The hammer is notched at the top of the strike face and is too low for the bolt carrier being used.

    What won't hurt a thing...
    Slightly file a couple thousands off the sear FRONT/FORWARD flat spot that sits on the trigger groove.
    This will allow the sear to move slightly forward and catch an 'Iffy' hammer (hammer spacing).

    What I recommend is a trip to a FULLY QUALIFIED gunsmith that has experience with this particular trigger group.
    Home builders and a questionable supply of lowers/trigger group parts keep qualified gunsmith busy, this is pretty frequent....
    I can't stress enough this trigger MUST be safe above all other concerns!
     

    Notalentbum

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    Since it fires a few rounds and stops,
    The question is does it stop cock or not?

    If it stops cocked, the disconnect isn't working, and the hammer is catching on the trigger sear.

    A free hammer, hammer not being pushed back far enough to catch disconnect, will always follow the bolt forward and has to be stopped by the trigger sear, which leaves the hammer cocked.

    I imagine what's happening is the 7.62x39 upper has a bolt carrier slightly higher up (in relationship to the hammer) and not fully pushing down the hammer,
    OR,
    The hammer is notched at the top of the strike face and is too low for the bolt carrier being used.

    What won't hurt a thing...
    Slightly file a couple thousands off the sear FRONT/FORWARD flat spot that sits on the trigger groove.
    This will allow the sear to move slightly forward and catch an 'Iffy' hammer (hammer spacing).

    What I recommend is a trip to a FULLY QUALIFIED gunsmith that has experience with this particular trigger group.
    Home builders and a questionable supply of lowers/trigger group parts keep qualified gunsmith busy, this is pretty frequent....
    I can't stress enough this trigger MUST be safe above all other concerns!


    This is exactly the type of post I was looking for in my initial post! A decent in depth explanation of possibilities. While I have read and looked a little, I don’t have an exact understanding of the complete trigger function locked in my brain. Saying it’s probably the disconnector didn’t really help me enough to get my head wrapped around it yet. JeepHammer’s post hasn’t given me the whole picture but it has gotten me a lot closer.
    I’m off the next couple days so this is high on my priority list, along with many other little projects.

    Thanks, Matt

    By the time I work through this, I will have a very good understanding of the trigger function. If I don’t work on one again for a couple years, I will be back where I am right now.
     

    JeepHammer

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    Questionable parts often have a stamped disconnect, stamping leaves a ridge on one side of the edge that often causes issues.
    Flattening out the front seat (seat not sear) sometimes fixes the issues since the seat hook can engauge the hammer a little sooner/deeper.

    When the firearm stops shooting because the hammer is forward it's a ifferent issue altogether, usually a bolt not moving far enough back (actual short stroke).

    I haven't seen the lower, I don't have enough information to make a diagnosis, so this is a general guideline.
    The disconnect is the cheapest piece of the trigger group, and it's where I start when people have multi-fire issues.

    I still suggest you find a military trained gunsmith that is familiar with this particular trigger group, it's so misunderstood by so many it's often screwed up and/or made worse.
     

    Notalentbum

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    A bit of new information today but I’m more lost than before!

    I looked over the trigger closely this morning but couldn’t find any thing really wrong. The only thing I saw was the edge of the sear was slightly rounded rather than dead sharp. Maybe a.005-.010 corner break. Trigger had a fairly clean break but rather heavy pressure. I had never messed with this trigger assembly so it wasn’t my amateur smithing.
    Since I saw nothing wrong, I decided to swap out the whole package. I had an old, relatively new mil-spec trigger in my safe so I put it in. Everything seemed to function fine on the bench. I loaded up to head over to Parabellum for another test. While I was packing the truck, I had an idea for an additional possibility. I grabbed my INGO lower that I built up as a precision AR.
    First three rounds I was careful to trap the trigger back. Next shot I purposely was sloppy on the trigger and I got a double. I tried two more times trying to get it to bump fire but it only would do doubles. Better than before but obviously still not right!
    From this, I’m thinking maybe an issue with the BCG so I swapped lowers to my well used INGO lower. It fired the balance of four mags without any issues and I was trying to make it bump fire.
    Now I’m more lost and confused.
    Ideas???
    Matt
     
    Last edited:
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