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AR15 Double Fire/ Slam Firing

Discussion in 'Rifle Country' started by General Disarray, Nov 7, 2012.

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  1. General Disarray

    General Disarray Member

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    I have an Olympic lower that I don't know its origins. I bought this Franken build a while ago, and it ran ok so far. The searches I've done on slam fires tell of the same test for releasing the hammer, holding the trigger and resetting the hammer, then letting trigger go. I've done that test and when I let the trigger go, the nose catches the hammer as it should. I just cleaned the bolt/firing pin completely clean with Gun Scrubber aersol and reoiled, and it still slam fired on the 4th round today; then over and over every few rounds. What else besides the trigger, bolt face fouling, or high primers can cause this?
     
  2. gotigers

    gotigers Member

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    What ammo are you shooting? Reloads, cheap surplus?

    How worn is the bolt?

    If the bolt looks ok, i would start with a trigger group. A trigger group is cheap and easy to replace.
     
  3. WinThePennant

    WinThePennant Member

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    I've always wondered about this. What are the main reasons that causes ARs to slam fire? Will they only slam-fire with a full-auto BCG?
     
  4. gotigers

    gotigers Member

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    The only difference between a full and semi BCG is a smaller cut out. Functionally they are the same. There is more mass, but that by it self shouldn't cause a slam fire. I have full auto BCGs in 2 of my ARs and have never had a slam fire.
     
  5. Ramone

    Ramone Member

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    debris under the trigger 'shoe'?
     
  6. Shawn Dodson

    Shawn Dodson Member

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    An intermittent problem can be a challenge to diagnose.

    I suggest you load a magazine with a single cartridge and seat it in your rifle. Fire several rounds, one at a time, using the magazine loaded with a single cartridge. Press and hold the trigger to the rear to fire each shot, then slowly release pressure on the trigger. The trigger will either reset or the hammer will drop completely. If you think the hammer dropped then press the trigger again. It will feel "dead". You can confirm that the hammer is uncocked by attempting to engage the manual safety. If you can't engage the manual safety then the hammer is indeed uncocked. You'll have to replace the hammer, the trigger or both.

    It sounds like a previous owner did a "trigger job" by honing the hammer notch or trigger sear (or both) and removed to much material in the process or the parts have since worn because the case hardened surface was removed.
     
    Last edited: Nov 7, 2012
  7. MtnCreek

    MtnCreek Member

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    It sounds like someone did a little 'trigger work' on it. I butchered an AR trigger group one time and after a few months, the engagements wore a little and started giving doubles. Replaced the trigger, hammer (this is the part I butchered) and dis-connecter and the problem was solved.
     
  8. W.E.G.

    W.E.G. Member

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    Looks like you just bought an LPK.

    Better get it before the panic-buying reaches full swell.
     
  9. General Disarray

    General Disarray Member

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    What's an LPK?

    I didn't know much about the triggers on these, so watched a few videos etc, and took mine apart. Photos below. All the edges look solid, and springs are strong. Disconnector looks good, as does it's spring (not sure how long it should be though). I did the test for holding trigger, reset hammer, and let it go: the nose caught the hammer as it should. Does anyone see anything weird in the photos (I know the 2nd pin is not in photo):

    [​IMG]

    [​IMG]

    [​IMG]
     
    Last edited: Nov 7, 2012
  10. WardenWolf

    WardenWolf member

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    I'm going to venture a wild guess here: mismatched parts. If the trigger group parts are from different manufacturers or batches, they can have different tolerances and not quite match up the way they should. The trigger seems to have a darker finish than the other two, which would support this.
     
  11. carbine85

    carbine85 Member

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    Your triggers parts might be out of spec. Check your pin holes and make sure they are tight. Also check the firing pin and see if it free floats or if it's too long.
    I haven't had a slam fire ever with any AR15. I have experienced it with an AK and SKS. One case was a sticky firing pin, another was soft primers. Both correctable and my own fault.
     
  12. adelbridge

    adelbridge Member

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    I would look at that disconnect first
     
  13. General Disarray

    General Disarray Member

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    What would I be looking for there?
     
  14. General Disarray

    General Disarray Member

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    I'm comparing the disconnector with the one inside an unfired lower I have, and that one has sharp square edges. This one in suspect is in fact all worn along the front edge that catches the nose, and even more heavily along one side versus the other. It wasn't obvious at first, but adelbridge's suspicion was correct, the front edge of the disconnector is worn all uneven. It's still catching the nose when I do that hold the trigger/set the hammer test, so I figured it must be good to go. Maybe its worn just enough to function sometime, but not always under firing conditions?
     
  15. pseudonymity

    pseudonymity Member

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    The disconnector and/or disco spring may just be worn out. The catch on the hammer where the disconnector latches looks a bit worn in the pics also, but it is kind of hard to tell with the pics.

    There is a lot more force and vibration under fire conditions then when hand cycling the bolt.

    You pulled the firing pin out and verified that the channel was clear also? Sometimes you hear about small pieces of popped primers getting caught b/w the pin and bolt and causing slamfires. I would not consider a worn disconnector causing hammer follow to be a slamfire, but that is kind of nit picking I guess.
     
  16. Redlg155

    Redlg155 Member

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    1- Replace the all the internals with a quality lpk. This is a relatively inexpensive fix.
    2. Make sure your free floating firing pin is indeed free floating and not sluggish with accumulated crud.
     
  17. Nanook

    Nanook Member

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    Reloads with soft primers may do that from what I understand. Federals, and some Winchesters have that reputation.

    I haven't seen it yet, but I hear of it from time to time.

    CCI makes primers specifically for ARs, the CCI #41.

    But you don't say if you're shooting factory or handloads.
     
  18. redneck2

    redneck2 Member

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    Different deal, but my friend had a slam fire with his AR. Reloads with Federal (soft) primers being single loaded. The bolt was released from locked position. Forward momentum without picking up a round to slow down the bolt caused the firing pin to hit the primer hard enough to ignite.

    I realize it's a different deal, but something to watch.
     
  19. meanmrmustard

    meanmrmustard Member

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    Way to start the panic buying!
     
  20. capnbob

    capnbob Member

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    AR trigger

    I just joined this forum to sell a Jewell ar trigger, still trying to figure out how to post an ad when I saw this post.
    I have an essentially new (less than 50 shots) jewell ar-15 2 stage trigger.
    I think it was @ $215 when I bought from Jewell.
    I have all original tools and intructions and a spare hammer spring.
    This is for an ar-15 and I have an ar-10,
    it worked in the 10, but is not made for it, so I'm getting a different trigger.
    It works perfectly, and is adjustable in both stages with a small allen wrench.
    I'm going to ask $150 when I figure out how to post,
    it would probably cure the slam fires and is very smooth and crisp,
    reportedly the best match trigger made for the ar-15,
    let me know if your interested.
    capnbob-wisconsin.
     
  21. Quentin

    Quentin Member

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    I'd also buy a LPK and then replace your trigger group. Odds are very high that will solve your problem. It's nice to have the extra pins, springs, etc. from the LPK just in case. Simple, cheap fix.
     
  22. Slamfire

    Slamfire Member

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    Slamfires from overly sensitive primers are a rare event. Rare enough that the Army took the early AR15’s through development and field testing before enough slamfires occurred that it got high level attention. Your rifle should not be slamfiring every fourth round based on the statistics of primer sensitivity alone. But, funny things happen.

    Constant slamfires are typically mechanical in nature, double check that your trigger mechanism is not following, and make sure your primers are below the case head.

    If that is not it, use CCI #41’s or Tula Milspec primers.

    It is a fact of historical record that AR15’s did slamfire, and incidentally still do. The Army lightened the firing pin and used a less sensitive primer.



    http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA953114

    Early heavy firing pin on top. Picture from AR15.com.


    [​IMG]
     
  23. briansmithwins

    briansmithwins Member

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    1) High primers if using reloads.
    2) That hammer sear looks more polished than most I see out of the box.

    If you're not shooting reloads change the trigger, hammer, and disconnector.

    Also, make sure you're not bump firing the rifle w/o realizing it.

    BSW
     
  24. Walkalong

    Walkalong Moderator

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    My RRA two stage trigger doubled on me twice at the range one day. I went home, took the parts out, threw them away, and ordered another trigger group. No problems since. I bought a Spikes. It is nothing special as far as triggers go, but it is a reasonable pull weight, reasonably smooth, and most importantly, it has been 100% dependable. If I need to buy another trigger group, I think I am going to try this one.

    Of course the best option out there is the Geisselle.
     
  25. awgrizzly

    awgrizzly Member

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    Scanned through the answers quickly so this may have been mentioned. Check the firing pin hole in the bolt face for the possibility of the firing pin getting stuck. The hole may look alright but be a tad enlarged. Also maybe try another pin... they're cheap.

    A thing I've had happen... using a two stage trigger I started to what I call diddle the trigger, that is only release it enough to regain the second stage. Holding the trigger right at the point where it gets released by the disconnector can cause double fires because the jarring of the rifle is enough to cause the sear to release. But I suppose you would know if you were doing that.
     
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