S&W model 19 misfires

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  • Charleybravo56

    Plinker
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    Aug 28, 2010
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    Hey all
    I have a model 19, 357, 4" barrel. My wife bought it used for my birthday 40 years ago (she's a keeper). I was shooting it with some friends and it misfired repeatedly with various factory ammo.
    Before I throw parts and $$$ at it, I wanted to bounce it off of you folks.

    Thanks
     

    Doug

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    First, make sure it is clean and properly lubricated.

    Then, check the hammer spring strain screw on the front of the grip frame. Tighten it 1/2 turn at a time until you get reliable ignition. Realize that increasing the hammer spring tension will increase the double action trigger pull.
    If you're unsure how this works, go to Numrich gun parts and look at the S&W Model 19 schematic.
     

    billybob44

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    Sep 22, 2010
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    Strain Screw...

    Usually this is caused by a VERY simple condition: The strain screw is the way that the Main Spring is tightened on a S&W K,L, and N Frame revolver. Your Model 19 is a FINE example of a K Frame.

    This screw is at the forward/lower part of the grip frame. You may?? need to pull off the grip to access if the front of the frame is covered.

    Be sure that this screw is tight/bottomed out.

    If this is not the problem, other "Most Likely" cause would be a weak main spring. These are very easy to replace by anyone who has had the side plate off of a Smith.

    If out of your league, ask out here on INGO for someone close to your location..Bill
     

    billybob44

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    billybob44, I mostly agree, but I don't believe the screw needs to be completely bottomed out.

    Hay Doug..Yes, the design of this is made to be bottomed out.
    NOW--Trust Me--I, and others have made this screw a little "Shorter" on the end that meets the main spring. Most of us have a few spare screws for this..HA HA..Bill.
     

    bgcatty

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    Sep 9, 2011
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    Hey all
    I have a model 19, 357, 4" barrel. My wife bought it used for my birthday 40 years ago (she's a keeper). I was shooting it with some friends and it misfired repeatedly with various factory ammo.
    Before I throw parts and $$$ at it, I wanted to bounce it off of you folks.

    Thanks
    If you are having problems with a S&W revolver you take it to the YODA of such weapons located in Rochester, Indiana at the Sand Burr Gun Ranch. Period!
     

    Drail

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    On a S&W revolver the actual firing pin energy is determined by that screw being bottomed out all the way and having a factory mainspring in place. Over the years these screws may tend to back out and your gun can become unreliable with certain brands of primers. CCI/Speer are the hardest to pop. On a range gun with Federal only primers you can get away with "adjusting" the tension screw but you must keep checking it because if it is not torqued down all the way it will loosen over time. There is a kit available that allows you to tap and drill the grip frame for a set screw that will lock the tension screw in place for competition use. On a carry gun you WANT as much tension on the mainspring as possible. If someone is trying to kill you you WILL NOT notice a heavy trigger pull.
     
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    Sagamore - One

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    There are other things to look at as well as the main spring screw. If someone has shortened the screw... try placing a spent primer over the end of the screw and retighten.
    Also check to see if cylinder is properly positioned in the frame opening. I have seen abused K frames with excess lateral play. Check firing pin nose for damage or signs of Bubba and his trusty Dremel. A certain amount of hammer momentum is required to fire primers. If hammer is bobbed it reduces the striking momentum of the hammer. Aftermarket spring kits do in deed reduce trigger pull but at the expense of momentum transfer to the primer. I also had one with the hammer itself that would not go all the way down into the milled hammer slot. Fired on single action, but not double action. Single action firing provides slightly more energy to fire the primer than double action.
    If still baffled ... go see Denny.
     

    Drail

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    "If the hammer is bobbed it reduces the striking momentum of the hammer". An old wive's tale that is absolutely not true. It only reduces the mass of the hammer. The energy to pop a primer all comes from the mainspring - not the hammer's mass. I have bobbed hammers for many years and never seen a failure to fire from doing it. Only if someone replaces the factory spring driving the hammer and that has nothing to do with the hammer's mass. Lighten the mainspring enough and you will see failures to ignite a primer even with the original hammer. Bobbing the hammer actually causes it to travel faster and strike the primer with more force. If the hammer was only accelerated due to gravity it's mass would make a difference - when it's driven by a spring all of the energy is being provided by the spring.
     
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    Sagamore - One

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    With regard to the relationship between hammer velocity and hammer weight
    (directly proportional to its mass – note that under the US system of units mass
    and weight are numerically different).



    The mainspring provides the force to accelerate the hammer to its terminal
    velocity. Spring force is at a maximum when the hammer is at the rearmost
    position, and at a minimum when the hammer is fully forward. This means that
    peak hammer acceleration is at the rearmost position (just as it moves off) with
    minimum acceleration at the foremost position (just before it is arrested by the
    body of the revolver). Hammer velocity is obviously at a maximum just before it
    impacts the FP. This acceleration relationship can be represented by the simple
    equation F=m.a where ‘F’ = spring force, ‘m’ is the hammer mass, and ‘a’ is the
    resultant acceleration. Because spring force is constantly changing throughout
    the hammer travel, calculus needs to be used to determine the final hammer
    velocity, and the equation to determine final hammer velocity becomes more
    complex.



    By bobbing a standard hammer you reduce the hammer weight (mass),
    consequently the acceleration of the hammer (for the same spring force)
    increases, and the final velocity of the hammer increases.



    When the hammer strikes the FP it has two physical properties that are both
    related to its velocity and its mass. Momentum = mass x velocity. Kinetic energy
    (KE) = mass x velocity x velocity. It is apparent from this that if the hammer
    velocity doubles, then the momentum doubles too, BUT the kinetic energy is
    quadrupled.



    With regard to primer ignition, a grey area arises because there is
    uncertainty within the industry (or at least those on the fringes of it) as to
    whether momentum or KE is the most important parameter for reliable ignition. It
    is most likely some combination of both, but if anyone has reliably determined
    it, I have not seen it published.



    All of this physics/mathematics is somewhat abstract to us average
    peasants, so it is best illustrated by practical examples. In the gun world,
    Ruger still offer the SP101 2.25” 357 with a regular hammer, or a spurless
    hammer. The spurless version is not simply the spurred one with the spur chopped
    off – it is a different shape so that the weight (mass) of the original hammer
    is duplicated. I’m sure that Ruger would not go to the trouble and expense of
    redesigning a hammer and making new molds to manufacture it if 2 minutes
    grinding on the standard hammer would suffice.



    Another example of the complex dynamic relationship between mass, velocity,
    momentum, KE, and desired results can be found with an example of pounding in
    fence posts. I can take a 1 pound hammer and hit a fence post with all my
    available energy, but the fence post will not be pushed into the ground. I can
    then take a 5 pound hammer and hit the post using the same effort, but this time
    the post moves into the ground. So in this example the hammer is the hammer, and
    my arm/body is the spring providing the force/energy to do the work. Same force
    / energy at my end, but different results at the business end. So in this
    example (not too dissimilar from a hammer moving a FP info a primer) momentum is
    clearly more important than energy.
     

    Bosshoss

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    I don't know where you copied that write up from but way to many errors and misrepresentations , like the formula for KE is wrong and that is the basis for the whole article.
    I'm not going to argue about something that has been debated(wrongly) for years.

    I will post what I know.
    I have been doing competition and carry action jobs on revolvers for years, and that is my retirement job now, and I shoot revolvers in competition every weekend.
    I have talked with other top gunsmiths in the competition revolver world and they have said the same thing.

    I know that 95% of the revolvers used in revolver competition have bobbed and reduced weight hammers(they don't do it because it looks cool). The other 5% are just stubborn or recreational shooters or haven't got around to it yet.:):

    I know that on my action jobs the lighter the hammer the lighter the DA trigger pull can be and still be reliable on centerfire revolvers. Rimfire's are a entirely different matter.

    I know that I have a gun that was 25% failure to fire with a full hammer in the gun. Just putting my competition modified ultra light hammer in the gun with no other changes it has been 100% for 35K rounds.

    I haven't done a test with several guns to get a precise figure but I would guess that with 100% reliability I can get one of my lighted hammers guns about 1-1.5 pounds lighter DA pull than a full hammer in the same gun.

    I know the company's selling aftermarket hammers for competition all are substantially lighter than stock.


    There are many things that can affect the reliability of a revolver as far as light strikes but a lighter hammer HELPS the reliability.

    I think every S&W revolver I have has a lightened hammer even my carry guns including a 642 internal hammer gun.

    A lot of shooters don't put the time and effort in learning the DA trigger pull of a revolver and they still like shooting them but SA. They don't want a bobbed hammer but I still can take a lot of the hammer weight out of a hammer internally so it doesn't show from the outside.

    While I specialize in tuned competition S&W revolvers the same Physics applies to any of them used for carry or hunting or general range use.
     
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    LCSOSgt11

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    Check strain screw to see if it is bottomed out...it should be. Check the hammer nose to see if it is not broken. On the older Smiths, the hammer nose is a replaceable part, as the older Smiths did not have the firing pin in the frame as they do now. It could also possibly be the timing, as the cylinder may not lock up before the hammer fails. If that is the case, the gun may need to go to a qualified gunsmith.

    Also, if you have shot a lot of magnum ammunition through the pistol, you may need to have it looked at anyway. Way back in 1982, I bought a Smith 66 4" and whilst at college, put a considerable amount of magnum ammunition through it. It was my first pistol and was used as a duty weapon, and after a year or so of shooting (we qualified with wadcutters at the time, and carried magnums for duty) it started having timing issues. I went through three sets of cylinder hands, cylinder stops, hammers, and triggers before it was timed properly. The K frames just don't hold up to a whole lot of magnum ammunition. Hence, Smith developed the L frame. The N frames never had the problem to begin with.
     
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    WeeJ

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    I hope the OP gets this sorted out - a lot of possibilities fielded, and lots of things to try. Looks like it may need some expensive gunsmithing whatever the problem is.

    Pleased I read this thread because I've been having a devil of a job beating roofing nails into new shingles in this summer heat. Thanks to Bosshoss I now know that all I need is a lighter hammer, not the heavier one I had been eyeing - go Bosshoss :-)
     

    Bosshoss

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    Pleased I read this thread because I've been having a devil of a job beating roofing nails into new shingles in this summer heat. Thanks to Bosshoss I now know that all I need is a lighter hammer, not the heavier one I had been eyeing - go Bosshoss :-)

    Not sure where you are going with this but if you are swinging new heavier hammer same speed as old lighter hammer then it will work better than the lighter hammer. Just like the fence post scenario above the heavier hammer will work better in that scenario because he said the hammers were swung with same effort as in striking velocity.

    Since this is about firearms and not fence post or shingles I will restate this.

    When you reduce the mass of the hammer and have the same spring tension as before the hammer accelerates faster and reaches a higher velocity delivering more energy than before.
    There is a reason most of the 1911 and revolver hammers sold are advertised as "lightened". Lighter firing pins and strikers in other guns also.

    WeeJ here is a tip if you are having trouble driving the roofing nails in then get a nail gun. The part that drives the nail in(just the piston not the whole nail gun) is nowhere near as heavy as your hammer but it does it with much greater velocity.:)
     
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