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Thread: Aim with variable power scope?

  1. #1
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    Aim with variable power scope?

    This might be a dumb question but I can't figure it out I need help!!

    So I have 4-16x50 mildot scope from Vector.(just a cheap scope)

    If i was to find a distance with this scope I have to use 10th power using mildot calculation.

    This is second focal plane scope so crosshair size don't change depending on the maginification.

    So if I shoot one mil above the cross at 10th power, will it be same if I shoot one mill above cross at 4th or 16th power?

    I was trying to figure this out for quite a long time now

  2. #2
    R93
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    No. Only works with FFP scopes.
    Your scope should have a set magnification the reticle will work on. Usually around 10x

    Sent from my SM-G900F using Tapatalk
    Do what ya want! Ya will anyway.

  3. #3
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    Hi,
    I wrote an article on this for NZ Guns & Hunting a few issues ago. Here is an extract from that article. I was demonstrating the use of a cheap MILDOT scope on a 22LR being used to shoot out to 200m without needing to dial the scope. The exact same principle applies for what you want and the formula still works if you want to use 16x and your MILDOTs. You will need to rearrange the equation below to make it work out what you want it to.

    The formula to work out how much to reduce the scope power is a straight forward ratio:

    SPR = (SPA A) / HOR

    Where
    SPR = Scope Power Required
    A = Aiming Point Hold Over
    SPA = Scope Power where the hold over is correct
    HOR = Hold Over Required

    For my example I want to use the 4th mildot under the centre of the cross hairs – this mildot is 4MIL at 9x power. This means for my example “A” is 4MIL and “SPA” is 9x power.
    My ballistic program estimates I will need 5.4MIL of elevation to hit a target at 150m. Using the above formula this means to use the 4th mildot I need to reduce the scope power to 6.7x power (9x4/5.4 = 6.7).
    DISCLAIMER!!!
    You need to test this theory on your rifle and your scope. I have no idea if your scope
    • has a correctly dimensioned reticle at the nominated magnification
    • that your scope actually magnifies the image the amount is says i.e. it is 16x when it says it is, and all the other power line up as well
    • that your scope does shift its point of impact when you change the scope power.
    GNAR likes this.
    You cannot miss fast enough!
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  4. #4
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    Quote Originally Posted by Gillie View Post
    Hi,
    I wrote an article on this for NZ Guns & Hunting a few issues ago. Here is an extract from that article. I was demonstrating the use of a cheap MILDOT scope on a 22LR being used to shoot out to 200m without needing to dial the scope. The exact same principle applies for what you want and the formula still works if you want to use 16x and your MILDOTs. You will need to rearrange the equation below to make it work out what you want it to.



    DISCLAIMER!!!
    You need to test this theory on your rifle and your scope. I have no idea if your scope
    • has a correctly dimensioned reticle at the nominated magnification
    • that your scope actually magnifies the image the amount is says i.e. it is 16x when it says it is, and all the other power line up as well
    • that your scope does shift its point of impact when you change the scope power.
    This is very useful info Thank you!!

  5. #5
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    Having a think about it (and assuming your scope reticle and power adjustments are perfect then 1 MIL at 10x is equivalent to below at 16x
    SPR = 16x
    A = 1MIL
    SPA = 10x
    HOR = (SPA A) / SPR = (10x1)/16 = 0.625MIL

    Just for interest the formula predicts that at 11.1x the angular measurement between your mildots will be equal to 3MOA. Handy to know if your scope adjustments are MOA and your reticle is in MIL!

    Again check the disclaimer!
    WallyR likes this.
    You cannot miss fast enough!
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  6. #6
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    Hi GNAR,
    I ve got a 4-16x second focal plane mildot (dots are 1mil at 10x)) scope on my airgun so have had the same geometrical challenge as you.

    I decided to use only 5x and 2.5x at lower powers so the dots are then 2 mil or 4 mil and relatively easier to remember or use in a hurry. I ignored ballistic calculators even though they are quite accurate because on a $200 scope i dont really trust either the reticle size or the magnification. So i shot at measured distances and recorded the number of dots needed. With the airgun this is mostly for shots at close ranges like 5 and 10m. And ammo is cheap.

    Ive actually found it easier to aim over an estimated number of cm on the target or to dial the turrets. You can reliably use a balkustic calculator to di this provided you calibrate it at a short and long range.

    Most people will need to use a pre made range card rather than live calculation from a formula in the field.
    GNAR likes this.

  7. #7
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    What am i talking about using 2.5x on a 4-16x scope ? Usually for linger shots i use 12x or 16x but to use mildots i wind back to 10x or 5x which is ok for short shots but in general top mag is best for shots beyond your sight in range. Winding back mag is a very second best solution and limts the effectiveness of all holdover reticles on SFP scopes. By the way mildots were originally designed for range estimation not holdover aim so they are a bit far apart for precise shooting.

 

 

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