Measuring scope height

Discussion in 'Long Range Hunting & Shooting' started by elkstalker300, Sep 25, 2009.

  1. elkstalker300

    elkstalker300 Well-Known Member

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    Was wondering how everyone here measures the scope height to enter in a ballistic program, I take it that it is from center of bore to center of scope but is that at the front of the scope or middle? I have my scope mounted on a 20 MOA rail and wasnt sure if I should measure it at the front of the obj. or more towards the center of the scope. Any comments would be helpful,

    WOOOOO HOOOOOO ELK season is only 3 weeks away
     

  2. nddodd

    nddodd Well-Known Member

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    +1 on that, I'm curious as well. Just watched both of Shawns videos and in one section he explained how to use the exbal program, which is where he said his scope height was 2.1" above bore. I always thought it was just 1.5" above so this has me wandering the same thing. If you haven't seen Shawns videos I highly recommend them, very informative and fun to watch.

    Nathan
     

  3. Autorotate

    Autorotate Well-Known Member

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    ES300

    Here are some threads a search turned up for reflection:
    http://www.longrangehunting.com/forums/f18/what-defines-sight-height-44859/

    http://www.longrangehunting.com/forums/f17/measuring-scope-height-using-canted-bases-42576/

    http://www.longrangehunting.com/for...ht-represent-hollands-software-program-35740/

    http://www.longrangehunting.com/forums/f18/measuring-scope-height-29019/

    http://www.longrangehunting.com/forums/f18/sight-height-measurement-23877/

    http://www.longrangehunting.com/forums/f26/scope-height-measurement-17568/

    I think you'll have a hard time coming up with a written reference/definition for this...your best bet if your after that would be to contact your ballistic software producer, and ask what their definition is/how it applies to your specific software.

    My opinion-If pressed for an answer, mine would be the "sight height" would be defined as the point/axis where the rifle is rotated when changes in the elevation turret were made on the optic in order to point or aim the rifle at the same target.

    Another thought-There might be more worthwhile things in your shooting system to dedicate time/thought too. It was calculated in one of the previous threads linked above that a 20 MOA base is less than .07 difference between the objective height and eyepiece height on a 12" scope....when I apply a .07 variation to sight height, I see no difference in dialed elevation adjustment out to 1500 yds. But like you....I can't stand to be ".07" off on anything:)

    BTW-Those two opinions wasn't formed from any scientific knowledge/analysis, or special prowess on my part, but rather from conversations with some LR "sages" on this board and others in the precision shooting community. My 2 cents...but just barely worth 2 cents:)

    Good luck!
     
  4. elkstalker300

    elkstalker300 Well-Known Member

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    Interesting because my program has a considerable differance in just one inch of sight height at 1000 yards, I will check out those links thanks. I am surprised that no one has chimed in with info, it is a common input on calculators so I thought everyone would have a say in this
     
  5. Novus9594

    Novus9594 New Member

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    That's only an issue if you have a 20 MOA Scope base. If you use a standard, level scope base, it won't make any difference whether you take the sight height at the objective lens or the center of the scope. (this is because when you adjust your scope, the reticle moves, not the scope itself, so the height for the center at the turrets and the objective remains the same, assuming level mounting.
     
  6. rscott5028

    rscott5028 Well-Known Member

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    It pays to be as precise as possible. But, you also have to keep things in perspective.

    You should be close enough if you measure from the centerline of the bore/bolt/firing pin to the centerline of the scope where the turrets are located. It may make it easier if you meaure top of the bolt to bottom of the scope and add half the scope diameter plus half the bolt diameter.

    Any such reasonable measurement should suffice as other shot to shot variables will present a bigger challenge for predicting POI at long range.

    e.g. 7RM+180 Berger @ 2600 fps
    1.8" scope ht=317.1" drop @ 1k
    1.3" scope ht=319.1" drop @ 1k
    2" @ 1000 yds < 1/4 MOA (less than 1 click on most scopes)

    How much change in MV do you get with a 20 deg change in termperature from the particular powder that you use?

    What MOA accuracy can you depend on from your rifle?

    JMO
    -- richard
     
  7. Autorotate

    Autorotate Well-Known Member

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    [​IMG]
     
  8. C.O. Shooter

    C.O. Shooter Well-Known Member

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  9. GMBshootingclubM60

    GMBshootingclubM60 Well-Known Member

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    Autorotate..

    You use a Near base on your Weatherby, correct?

    How many and what size attaching screws does it use?

    You use a 30mm scope, right?

    I have copied what you're doing, just got the Bell&Carson stock.

    That way I can save newbie time!

    Willy
     
    Last edited: Aug 11, 2011
  10. Bigt243

    Bigt243 New Member

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    Depends on the program. Knights bullet flight is from top of rail to center of scope.
     
  11. Bravo 4

    Bravo 4 Well-Known Member

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    Interesting. Where did you get that info? We got that program with the M110 SWS kits.
     
  12. Bigt243

    Bigt243 New Member

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    I called knight arm. And talked to there tech support.
     
  13. Bravo 4

    Bravo 4 Well-Known Member

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    I had spoke with one of them before and wasn't too impressed. It's something I will look into, maybe read the directions.:rolleyes:
    Thanks again, if for some crazy I find something different I'll let you know.
     
  14. 4xforfun

    4xforfun Well-Known Member

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    Firguring scope height is simple math. Start with a disasembled gun/scope/rings/basses.

    First....find the diameter of your action.....ie Rem 700 is 1.35"...divide that by 2 = .68"

    Second..... figure out the diameter of your main tube on your scope and divide it by two...1" tube = .5 ....30mm tube (1.18" divide by two) =.59"

    Third, measure how tall your base/ring combo is from where it mates to the reciever to the BOTTOM of the rings where the scope tube sits. lets say it is .75"

    now total up your figures...1/2 dimater of action + 1/2 the diameter of the scope tube + ring/base height............ (.68 + .59 [30mm] + .75 = 2.02" scope height.

    It really doesn't matter which base you measure if your rings/bases are tapered unless you are ULTRA ANAL!!! If you are, then measure both of them and divide by two the get your ring/base height.

    And to the guy who said the the bullet drop is different (317.1" vs 319.1") based on scope height...HOGWASH.....bullet drop is bullet drop is bullet drop. The bullet leaves the tube and drops xxx.xxx.....the bullet does not know weather there is a scope on the gun. Now, IMPACT POINTS will be different because you are sending the bullet out on a different trajectory.