scope expansion

Discussion in 'Competition Forum (All Calibers)' started by Alex Wheeler, Oct 29, 2016.

  1. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    Measured the length of a 12-42 br scope over 40 degrees on my granite plate with a height gage. It grew .009". FYI, take from it what you want.....
     
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  2. JRS

    JRS Silver $$ Contributor

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    Like steel, aluminum expands and contracts with temperature.
     
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  3. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    Haha, I think we know that... The point is to think about how this effects scope mounting and accuracy ;)
     
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  4. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    A panda action is cooling right now for the next measurement. I know here at deep creek we can easily see 40 degrees from day to day.
     
  5. JRS

    JRS Silver $$ Contributor

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    As long as the glass isn't mounted directly to the tube, it shouldn't make a difference. Cheaper optics might be mounted directly to the tube. Higher end optics are probably using an adhesive that eliminates direct contact so that the glass doesn't tilt forward and backward with expansion and contraction. Nightforce is a good example. No direct contact with the tube.
     
  6. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    Agreed. My though was more along the lines of stress. We go to lengths to make certain the bedding is not stressing the action in any way. The expansion of a scope will put the exact same stresses on the action. Just thinking out loud.
     
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  7. JRS

    JRS Silver $$ Contributor

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    Well then…perhaps we should use slotted holes in the scope ring bases;) As long as the expansion and contraction happens in a straight line, I doubt we have anything to worry about.
     
    Last edited: Oct 29, 2016
  8. 308sawyer

    308sawyer Silver $$ Contributor

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    How much did the height gauge grow?
     
  9. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    The height gauge didnt change temp. The scope was in a freezer.
     
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  10. joshb

    joshb Gold $$ Contributor

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    I just thought the change in accuracy was from me, shivering.
     
  11. fredhorace77

    fredhorace77

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    I better get my patent going on my new invention, A fleece down scope coat:p:D
     
  12. LRPV

    LRPV Jason Walker Gold $$ Contributor

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    Carbon fiber scope tubes anyone?
     
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  13. 308sawyer

    308sawyer Silver $$ Contributor

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    A very ingenious test, now how does one counteract the effects of such expansion if it does effect shot placement?
     
  14. 500Stroker

    500Stroker Silver $$ Contributor

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    I wonder how this may or may not effect parallax?
     
  15. JRS

    JRS Silver $$ Contributor

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    Atmospheric conditions are much more important than the expansion of a scope tube. It's nothing to worry about.
     
  16. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    Please explain the testing you have done to back this statement..... I am not saying what effect this has because I have not tested it. However, if I have a high spot in my bedding and tightened the action down it will bend. A force pushing the rings apart will do exactly the same thing.. how much and will it show on paper, I dont know.
     
  17. JRS

    JRS Silver $$ Contributor

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    I witnessed the late John Adams test this with Stu Harvey present. They used a bore collimator. Using software in a computer, it showed a difference of 3/32" at 2500 yards. Atmospheric conditions play a much bigger role. To spread the rings apart is certainly going to show up on the scope tube, and the rings!
     
  18. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    How was the test performed? Im not familiar with it....
     
  19. JRS

    JRS Silver $$ Contributor

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    I'll
    I'll try to contact Johnny (John's son), and ask him to froward the documenting paperwork that John retained. Each and every step was documented. John was quite an innovator, and Stu Harvey, a great rifle smith, shooter and competitor.

    Edit: Alex, the test pertained to the barrel also, to determine whether anything changed while/after the barrel expanded in length.
     
    Last edited: Oct 30, 2016
  20. Albany Mountain

    Albany Mountain

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    Shoot hotter!
     

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