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  • MST 100 binding up

    Need some help/advice guys I have a MST100 that is binding up solid at 4 MOA windage, the scope is hardly used since new less than 200 rds and never needed to dial past 4 moa before the other day and to my dismay it bound tight as a drum just past 4

    Anyone have a idea what it could be as I am in Australia and shipping back to USO is a pain in the ass, and it is way out of warranty now even though it has been hardly used.

    all help greatly appreciated

  • #2
    Cant provide any ideas other than guesses but TokiWarTooth has had the balls to take one apart and has good knowledge of whats inside these tubular wonders hopefully he will chime in.

    More than 4MOA wind? Sounds like a day to have maybe watched some rugby with a few Fosters mate.
    "...But they would never find anything to beat the old Springfield ...the long sleek streamline, very slim but with potent bulges, all in the just exactly right places to give it that pugnaciously forward-leaning, eager look that marked the Springfield. Beside it, the M1 looked like a fat old man puffing with a lack of training...the two most beautiful things made in America were the ax-handle and the clipper ship? ...they should have added one more thing: The Springfield '03 rifle..."

    Comment


    • brent65
      brent65 commented
      Editing a comment
      Yeah i hear ya, but it was good practice 700 yds from a hill across a gully and small lake with a cross wind @ 15 mph gusting to 20+. I got 47 hits from 60 rounds on a steel 16 x 20" plate so relatively happy considering how little i actually shoot this rifle

    • SemperFi
      SemperFi commented
      Editing a comment
      The first Unertls only had 4 1/2 MOA windage adjustment, and were designed to be used using the mil dots. Each mil dot spacing is about 3 1/2 MOA. There have been many times I've had to use the dots to supplement windage values needed.

  • #3
    Is it the Primary Large Windage or the Fine tune?

    One possibility is the detent ball came loose inside the turret.

    Does it still look straight? If the Primary Windage Screw (large screw you use to zero) is bent that would be another reason. (have you dropped it hard?) I had to replace my elevation screw because of that. Not too difficult Just need patience and the part.

    Another possibility is If you tightened down the locking screw too hard at one point it could have messed up the threading and that could be binding it.

    Add some pictures if anything looks out of place

    Comment


    • brent65
      brent65 commented
      Editing a comment
      No fine tune on the windage but everything looks normal and it hasnt been dropped if i had a pic of the internals maybe I would attempt to pull it down but i dont want to screw it up further

  • #4
    When you say "bound", do you mean it won't go past 4MOA, or that it won't turn at all now? Also, were you able to turn past 4MOA previously with no issues?
    Last edited by SemperFi; 11-11-2017, 03:13 PM.
    You can take a Marine out of the Corps, but you can't take the Corps out of a Marine.

    Comment


    • brent65
      brent65 commented
      Editing a comment
      I am not sure if i checked full travel on this scope previously as it is on my A1 which doesn't come out much. Everything on the scope works as it should except the RH windage stops at slightly past 4 moa and wont go any further and if I try and apply force it locks tighter, LH hand windage is no issue has full travel.

  • #5
    It could be the detent ball binding as it moves out of its hole. Which may be because the knob was not assembled to the scope far enough. It maybe should have gone down another turn.

    Or, it could be due to a manufacturing defect if the limiting slot was not completely machined.

    Either way, there's no easy fix unless you're willing to take a chance. If you have a depth micrometer, check the depth of the center adjusting screw from the surface of the windage knob as it is now, and report that depth here.
    You can take a Marine out of the Corps, but you can't take the Corps out of a Marine.

    Comment


    • brent65
      brent65 commented
      Editing a comment
      .075" on the scope that is binding and .063" on my other MST100 that is working correctly

  • #6
    Originally posted by brent65 View Post
    "if i had a pic of the internals maybe I would attempt to pull it down
    You mean like this?.....
    patentimages.storage.googleapis.com/pdfs/US4247161.pdf
    You can take a Marine out of the Corps, but you can't take the Corps out of a Marine.

    Comment


  • #7
    Originally posted by brent65 View Post
    .075" on the scope that is binding and .063" on my other MST100 that is working correctly
    O.K. Some good news, and some bad news. I think I might know your problem.

    Mechanical windage center on my Unertl is ~.040" deep (top of adjusting rod to knob face).
    Windage center on my mounted USO is ~.064" deep. (Mounted center is not usually mechanical center)

    One full turn of the windage knob should be about .025" (if my measurements, calculations and notes are correct from before).

    The MST100 working correctly at .063" deep sounds about right for a USO MST100 (mine is .064"), though those are mounted centers, not true mechanical centers. It's not really right to compare mounted zero settings like this.

    The MST100 in question at .075" deep is pretty deep. It may mean the windage knob should have been turned in one more turn, which would make your adjusting rod .050" deep at zero. If it is possible to turn it in another turn, then it may be your detent ball is coming out of its hole and binding. It's a possibility. Not saying it is the problem, but I have my suspicions.

    ON THE OTHER HAND, if the detent ball is coming out, one would think it would come all the way out and not just bind at that point. So, let me think on this some more.
    Last edited by SemperFi; 11-12-2017, 02:59 AM. Reason: Difference between mechanical center and mounted zero center.
    You can take a Marine out of the Corps, but you can't take the Corps out of a Marine.

    Comment


    • brent65
      brent65 commented
      Editing a comment
      thanks so much for your assistance

  • #8
    You're welcome. PM sent.

    I still think it is the detent ball binding. The knob rises so slightly, that as the ball moves in and out of each detent, the ball will also rise slightly more with each "click". I can envision the ball finally rising to the point that it rolls toward the edge of the hole as the knob is screwed out, and eventually it gets to a notch that as it is being pushed back into the hole it just hits the edge of the hole enough that it will not slide back down into its hole and binds. It would take a bit more rise of the knob for it to actually pop out of the hole altogether. That's my take on it- the knob should have been set down one more turn.

    Tokiwartooth may have some more ideas on your problem. He's had several further apart and knows his stuff.

    Here's what you have inside. The detent ball is not pictured, but rests on top of the small spring.




    You can take a Marine out of the Corps, but you can't take the Corps out of a Marine.

    Comment


    • #9
      thanks again to everyone for the advice especially a big shout out to SemperFi, I found the problem when i beginning the process of disassembly.

      The limit screw was too long.

      When I went to remove the windage limiting screw i found it loose so i tightened it, this in turn locked the windage drum solid would not move one way or the other. So I backed it out one turn and the tried drum rotation again and like magic everything functioned as it should have. So I removed the screw, filed then stoned 1 thread off the bottom off it, reinstalled and now it works like a charm.

      Comment


      • SemperFi
        SemperFi commented
        Editing a comment
        Nobody seems to make things like they used to. Even otherwise reputable companies turn out lemons these days. Disappointing.

    • #10
      I'm glad you got it figured out and fixed. As it turns out, I was giving you useless information. When you said it would bind when turned RH, I erroneously thought you meant turning the knob to move the POI right, which is turning the knob out, or to the left. My bad. Either way, it turned out to be a much simpler fix and you're good to go now, and you have the old patent drawings filed for future reference.
      You can take a Marine out of the Corps, but you can't take the Corps out of a Marine.

      Comment


      • #11
        Unertl Rifle telescope Patent.docx

        Here's the whole thing! (testing the attach document function)

        Comment


        • pmclaine
          pmclaine commented
          Editing a comment
          Date on the drawings is Jan 27, 1981.

          My 13th birthday.

        • SemperFi
          SemperFi commented
          Editing a comment
          Which is interesting, since the first contract scopes were delivered nearly a year earlier, and the prototypes before that.

        • brent65
          brent65 commented
          Editing a comment
          I cant get it to work, opens momentarily then closes

      • #12
        It’s .docx format so if you have an older version of word it may be a problem.

        File date was in 1979 I think... that may have been the provisional and not had drawings as the design was refined- no football knobs for windage in the drawing for example...

        Comment


        • SemperFi
          SemperFi commented
          Editing a comment
          Good point. Didn't catch the 1979 filing date. So, then the patent was finally granted in 1981?
          No need to change the drawings to reflect the knob shape changes, as the exterior contours of the knobs were not part of the patent. This patent was strictly for that little ring and associated parts that are used for elevation fine adjustment. These patent drawings are straight from the original prototype scopes, even down to the stacked elevation knobs.

      • #13
        It might have been granted later. Now-a-days it is at least five years depending on complexity. I’m sure you can get the exact date from the patent office.

        Comment


        • #14
          Ball probably came out, is sitting in the stop screw hole, and the spring is grinding up.

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