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How to test for push off when buying a used S&W

Discussion in 'Handgun Discussion' started by PhysicsGuy, Jan 1, 2010.

  1. PhysicsGuy

    PhysicsGuy Corvallis, OR Resident Science Nut

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    I always tell people to check out smiths thoroughly when buying to look for bubba trigger jobs or other tinkering by people who don't know what they're doing. But I made the mistake of forgetting to check for one thing with the last smith I bought. I usually check for a condition called "push off" some people may be familiar with it, others may have no clue what I am talking about. Push off occurs when there is negative engagement between the hammer and trigger, this can be caused by substantial use, or someone with a file thinking that they are doing a trigger job. Typically you want your trigger to have a slightly positive engagement, but only very slightly, too much and you end up with a trigger that is stacking. On S&W's a negative or neutral engagement is unsafe and should not be acceptable for use.

    Anyways, as it turns out, the one smith that I don't test for happened to have push off. Push off is a condition where when the hammer is locked back (single action), the negative engagement of the hammer and trigger allows the hammer to fall if pressed, gun is dropped, ect. This is an extremely unsafe condition, and if you have a S&W with this problem, do not use it (as in firing live ammo) until it is repaired.

    The best way to test for push off is to have the gun apart with the hammer and trigger springs removed, this is to remove all outside influences. But if you're just checking out a gun, this test is still satisfactory. To test, first assure the firearm is unloaded, check twice, then lock the hammer back as if shooting in single action. Then with your thumb press forward firmly on the rear of the hammer spur, as if you are trying to force the hammer forward to fall. Do not use an excessive amount of force (less that 10 pounds or so) because you can actually cause the condition by applying too much force and damaging your trigger engagement. If the hammer falls forward with this pressure, then your gun has push off. If I had a video camera, I would have demonstrated before I repaired my gun.

    Now as far as repairs, the best part to repair is the trigger, if your gun has a case hardened carbon steel (or MIM) trigger, then you can simply re-stone the angle on the trigger edge to return a positive engagement. Although you may remove the hardness from this edge (but the case hardening is pretty thick as well), the carbon steel is strong enough to take the wear, and there is enough surface area on the other trigger edge to give a secure engagement.

    Now if you have a revolver that has a stainless trigger that is hard chromed (it will be a light gray, and is found on earlier stainless guns), then you cannot solve the problem correctly by simply regrinding the edge, it may be a temporary fix, but without the hard chrome, the stainless steel will not hold this edge correctly. The best way to rectify this problem is to just buy a new trigger (but since they do not make these triggers anymore, you may have to do with an unmolested used one). All you will have to do is pop off your cylinder hand from your old trigger, and put it on the new one. Minor fitting on the fitment pins may be required depending on where the trigger came from. Also if you want want to improve the trigger feel slightly, you can buy oversized pins, and fit them to your gun.

    I hope this helps you guys out with what to look for when buying a used S&W revolver, and what to do if you end up with one that has this condition.
     
  2. eriknemily

    eriknemily Tillamook County (Cheese!) Member

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    Thanks PG. That's some great info to file away. I'd never heard of 'push off' before:thumbup:
     
  3. jmh119

    jmh119 Hillsboro, Oregon Member

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    Thanks PG, I learned something new! Now, should I happen to have this condition in one of my pistols, how much would you charge to teach me how to fix it? ;)
     
  4. MountainBear

    MountainBear Sweet Home, OR Well-Known Member

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    Its more of a glancing push on the hammer, not a hard push to the back. Its almost like slipping your thumb off the back of the hammer spur. It should be done from the left, center, and right, not just one push from the rear. I would estimate the weight of the push to be more like 5 pounds. Be careful doing this in a shop. If you don't know what your doing and push too hard, you just potentially ruined a hammer or trigger and have an upset shop keeper.

    The Kuhnhausen manual lists the fix for pushoff as replacement of hammer or trigger.
     
  5. PhysicsGuy

    PhysicsGuy Corvallis, OR Resident Science Nut

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    The one that I had took a little more than 5 lbs to fall, but it wasn't suffering from it super bad. Close examination of the trigger shows that someone took a stone/file to the trigger, most likely trying to do a "trigger job".

    But I do agree that too much pressure is a bad thing since you can damage the parts. And yeah it is more of a push upwards and forward, glancing your thumb off the hammer is a better definition :D

    Best solution is replacement, although the case hardened triggers can be repaired, and a trigger will run you around $40-50. Also 99% of the time it is because of the angle on the trigger end, but it can be caused by a worn/modified hammer, so a close inspection is required. (the single action notch on the hammer is very very small)

    In my case I just threw a new trigger in, and it fit as good as the factory one.



    Thanks for the added advice mountainbear!
     
  6. PhysicsGuy

    PhysicsGuy Corvallis, OR Resident Science Nut

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    I'm not a certified/qualified gunsmith, but if you feel confident, replacement is pretty easy to do yourself. But getting the opinion and inspection of an experienced gunsmith once you have it apart, and before you go ordering parts, is always a good thing to do before you buy something that you might not need. Also I believe there are a few gunsmiths on this board, or at least one that has an ad here.
     
  7. Riot

    Riot Benton County, Washington Well-Known Member

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    Good read...
     
  8. MountainBear

    MountainBear Sweet Home, OR Well-Known Member

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    Always happy to help. In my experience, if you hand a revolver to several gunsmiths, each is going to test push-off different.

    When I was in school, I did a very light trigger on a comp gun. The instructor who graded the gun failed me on the project because of push-off. I had several of the other instructors check it and none of them had it fail push-off. The bottom line is that its a very good and important test to perform when buying a used S&W, but its very subjective as well...
     
  9. twoclones

    twoclones Tri-Cities, WA Well-Known Member

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    Interesting stuff. A video would have been great!
     
  10. BlvdKing

    BlvdKing Almost Boring Member

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    good information I just learned about this a month or two ago... I haven't owned many revolvers
     
  11. Gunner3456

    Gunner3456 Salem Well-Known Member

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    Good read. I didn't know that. :thumbup:
     
  12. roguebowhunter

    roguebowhunter medford Member

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    nice post ... learned somethin new .. Don