S&W trigger "backlash"?

Discussion in 'Gunsmithing and Repairs' started by Offfhand, Jan 8, 2018.

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  1. Offfhand

    Offfhand Member

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    The trigger on my S&W M-57 sometimes (more frequent recently) forcefully jumps forward when I fire (pulling trigger) from cocked position. Hammer fall is greatly reduced at same time. It works normally when fired double action. Is this something to be returned to factory for repair or something for local gunsmith? What is cause of problem? thanks for any help.
     
  2. WrongHanded
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    WrongHanded Contributing Member

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    When you shoot in single action, and the trigger is forced forwards as you describe, does the gun fire?
     
  3. Offfhand

    Offfhand Member

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    No it does not, the hammer is falling at the same rate as the trigger is moving forward. It feels like double action in reverse.
     
  4. WrongHanded
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    WrongHanded Contributing Member

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    That's what I thought. I am by no means an expert on the internal working of the DA/SA trigger/hammer system. But it sounds like what (I think) is called the 'double action hammer dog', is catching on the DA sear of the trigger as the hammer releases.

    How that could be happening, I don't know. If it were me, I'd disassemble the gun and take a look. But that's a decision you should make for yourself. Whether to send it to S&W versus a local smith is hard to say. It could just be something sticking, or a part could be broken or worn and need replacing.
     
  5. farm23

    farm23 Member

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    I would call S&W and ask their advice. They may want the gun back.
     
  6. MrBorland

    MrBorland Member

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    If the hammer and trigger are still free to return without binding, @WrongHanded, might be right, though I think he's mixing up the locations of the sear, etc.

    Check out the pic below. What I think @WrongHanded is suggesting is that the hammer's DA sear is catching on the trigger nose as the hammer's falling, which might be caused by a DA sear that's too long.

    What's confusing to me is why it "sometimes" does it. Maybe a worn/cracked hammer or trigger pin? That'd definitely be a trip to S&W.

    If this (sear/nose interaction) is what's going on, I'm also confused on why DA function would be unaffected. Seems to me if the DA sear were this long, it'd hit the trigger nose after the hammer starts coming down as well, though I'd actually have to have an opened gun in front of me to look at clearances, etc.

    If the hammer and trigger bind up rather than freely returning, I tend to think the SA sear is binding against the trigger cam as the hammer's falling. I just described that in a recent thread as a faux half-cock, something S&W's are definitely not engineered to do.

    HammerStart.jpg
     
    Last edited: Jan 8, 2018
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  7. WrongHanded
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    WrongHanded Contributing Member

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    Yes, I have very little knowledge of terminology in this department. I pretty much take things apart and see how they work, whilst shamefully never learning the correct names of parts. Part 'A' is what I was thinking of. Some company that makes various shims had an arrow pointed to that part and referred to it as the "Double Action Hammer Dog". But if DA sear is the correct terminology, I'll try to remember that.

    I was thinking on the 'why' of the problem earlier. If it is the DA sear that is catching on the trigger nose, perhaps the retaining pin for the DA sear is bent or half way out (as MrBorland said), so that sometimes it sits farther forward than it should. That might allow it to catch in SA, but move up and away in DA. Which might result in the DA pull being shorter than it used to be.

    Or it could be something else entirely.
     
  8. d'zaster

    d'zaster Member

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    I'd call S&W. That ain't right.
     
  9. Offfhand

    Offfhand Member

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    Thanks for everyone's help. As suggested, I removed the sideplate and see the cause of the problem but don't see how to correct it as yet. Thanks again
     
  10. WrongHanded
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    WrongHanded Contributing Member

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    So what WAS the cause?
     
  11. Offfhand

    Offfhand Member

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    DA dog catching on sear.
     
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  12. Jim Watson

    Jim Watson Member

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    Did you back way off on the strain screw to "adjust the trigger pull?"
     
  13. BBBBill

    BBBBill Member

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    Uh, oh! Bad juju!
     
  14. Kp321

    Kp321 Member

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    Sounds like there is too little over travel after the SA sear breaks. Some Smiths have a small tab behind the trigger while later ones have a rod inside the rebound spring to limit over travel. Remove whichever stop yours has and see if it fixes it.
     
  15. Varminterror

    Varminterror Member

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    Sure startles you when that happens, don't it? Not used to getting kicked in the finger upon the shot! Wrong angle or excessive length on the hammer dog. Pretty simple fix, but most of the major OEM's make them come home for it. I pick up spare hammers and other lockwork for common revolvers when I can find them, so I generally just swap them around. Can be cut from barstock too, but it takes more time than it's worth most of the time.
     
  16. Offfhand

    Offfhand Member

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    Wow! just discovered when counting SA pulls. It fires (hammer falls normally) every 6th pull. So there is obvious relation to cylinder rotation/position. So I'm guessing it is related to DA dog and cylinder position. But how to fix it?
     
  17. Varminterror

    Varminterror Member

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    Mark the side of the cylinder and the recoil shield after the hammer falls on that particular cylinder to indicate it. Open it, spin it, close it back up, and repeat. I've been working on revolvers for a long time, and have ran into that particular DA sear issue dozens of times, but there's no real relation to the cylinder position. I'd be making up some BS to say it could be something in the tolerance relationship between the trigger, pawl, and indexing ratchet, allowing the trigger different travel for ONE cylinder, but even grasping for that, again, I know it's nothing but grasping BS, and if you fix the real problem - the DA sear - all 6 will go bang.

    If you're getting shoved by the trigger when the hammer falls from SA, and the hammer stops, the only failure mode is an over length or over angle hammer dog (DA sear). There's not enough mechanical "time" between the DA sear and the SA sear break for the DA sear to clear.
     
  18. Offfhand

    Offfhand Member

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    Thank you Mssrs. WrongHanded and Varminterror for information and regarding problem with my M57. I removed sideplate so I could see interaction of parts and your analysis is on target.
     
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