Tactical 4.0 120mm grip main spring

Discussion in 'STI/2011' started by cdholmes, May 17, 2019.

  1. cdholmes

    cdholmes Member

    53
    Apr 28, 2019
    I picked up a 120mm grip from Extreme Shooters to replace the 126mm on my Tactical 4.0. Everything was good until I put the main spring into the new shorter mainspring housing. Now the hammer is almost impossible to pull back. Is there supposed to be a shorter main spring for a shorter grip? I ended up cutting a couple of coils off the spring and it didn’t help. If anything I’ll probably pick up a Wolff aftermarket spring and try it.
     
  2. ChuckC

    ChuckC Well-Known Member Supporting Addict

    Feb 2, 2016
    You need an officer length main spring
     

  3. cdholmes

    cdholmes Member

    53
    Apr 28, 2019
    Any weight recommendations?
     
  4. ChuckC

    ChuckC Well-Known Member Supporting Addict

    Feb 2, 2016
    Factory standard for Colt is 23. That’s what I use. STI usually runs lighter on theirs, 19-21 I think. If you give them a call they’ll be more than happy to help IMO


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  5. Descartian

    Descartian Well-Known Member

    Apr 13, 2017
    I went with a reduced power on one of my Tacticals. I believe it was a 17lb or 18lb spring. I did this in conjunction with a flat (or low radius) firing pin stop.
     
  6. cdholmes

    cdholmes Member

    53
    Apr 28, 2019
    What brand did you go with?
     
  7. Descartian

    Descartian Well-Known Member

    Apr 13, 2017
    It’s been a while but I believe Wolf or Wilson.
     
  8. Descartian

    Descartian Well-Known Member

    Apr 13, 2017
    I stand corrected. My memory failed me but my organization did not. Found it filed in my small parts box.

    74011521-2E5E-476E-BA36-B6A2D46F6D8D.jpeg 8FCE0E0F-DE93-4C27-9004-DA09E863C883.jpeg
     
    Last edited: May 22, 2019
  9. cdholmes

    cdholmes Member

    53
    Apr 28, 2019
    I emailed STI and told them my situation. They said a 15lb officer's spring. That is pretty light is it not?
     
  10. Descartian

    Descartian Well-Known Member

    Apr 13, 2017
    For a mainspring or recoil spring? 15lb sounds light for a mainspring but they’d be the experts.
     
  11. cdholmes

    cdholmes Member

    53
    Apr 28, 2019
    I purchased 3 Wilson Combat compact main springs to test some different weights, but all of them are too big to fit into the housing. This is a lot more difficult then I thought it was going to be. I’m still in contact with STI so maybe they have a spring that will work. I know the DVC Carry comes/used to come with a 120mm grip, so whatever spring they used in that should be fine.
     
  12. ChuckC

    ChuckC Well-Known Member Supporting Addict

    Feb 2, 2016
    Describe what you mean by too big to fit in the housing?


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  13. cdholmes

    cdholmes Member

    53
    Apr 28, 2019
    The diameter of the Wilson Combat springs is larger than the hole in the housing.
     
  14. ChuckC

    ChuckC Well-Known Member Supporting Addict

    Feb 2, 2016
    Gotcha. That is strange. I would see what Dawson Precision has for springs.


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  15. cdholmes

    cdholmes Member

    53
    Apr 28, 2019
    I ended up cutting down the stock main spring from the 126mm grip and putting it in the 120mm housing. However, I’m afraid the hammer doesn’t have enough pressure behind it now.
     
  16. Descartian

    Descartian Well-Known Member

    Apr 13, 2017
    I ran into the same problem with Wilson springs. The must cut the spring tunnel in their MSH’s larger than average.
     
  17. Descartian

    Descartian Well-Known Member

    Apr 13, 2017
    cdholmes,

    Sorry,

    I did not get a chance to disassemble and compare a 120mm vs 126mm assemblies before leaving the country.

    You might want to reach out to Dawson Precision to order you a stock 120mm 9mm mainspring. Dawson has always been a good source of STI parts. I would think even more so now that he is in charge of quality control at STI (he’s a firmer STI master smith).
     
  18. Descartian

    Descartian Well-Known Member

    Apr 13, 2017
  19. gun_fan111

    gun_fan111 Well-Known Member

    Mar 23, 2014
    First let me say that I would very much like to see the pictures of a Tactical (4.0?) with a 120mm grip.

    Second, if you have calipers you can measure the diameter of the Wilson springs you got and we can compare them to Wolff springs I should have in my parts box.

    Finally, I agree with those that say 15 lbs sounds too light for a mainspring. I realize there is Recoil Master system in play here, but I would personally try 21-23 lbs first and stay with that if the gun runs 100%.
     
  20. Descartian

    Descartian Well-Known Member

    Apr 13, 2017
    On a 4.0 with a full sized grip, I have been running a 17lb mainspring for 1000’s of 9mm rounds in various weights.