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Switched scopes...now a little maths problem!

Discussion in 'Anything Airgun Related' started by Dag, Aug 23, 2014.

  1. Dag

    Dag Pro Poster

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    I've been using a Hawke 4-16x 50 IRAO scope on my TX200HC and have just realised I can make pellet loading much easier by switching to the Hawke 3-9x 50 IR that I had on my Meteor as it is shorter and clears the breech by an inch or two.
    The problem is, and perhaps I shouldn't be thinking of these things late in the evening, that whereas I have been using 10x on the 4-16x scope I will now be restricted to a maximum 9x on the 3-9x.
    So the first question is whether one mildot at 9x is now 10/9 x 3.6" at 100 yds ie 4" per mildot? Secondly, if I am wrong with that assumption how do I check what it is?
    Dag :confused:
     
  2. Jackroadkill

    Jackroadkill Donator

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    Have you got Chairgun? If so, input a change in magnifications and compare the mil-dot graphs.
     
  3. Snipertez

    Snipertez Donator

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    It will probably make a small difference and more noticeable at longer distances. To check, put out some targets and shoot :rolleyes: this will enable you to double check chairgun also, as above :)
     
  4. Dag

    Dag Pro Poster

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    Ok, thanks for the replies. I have tried Chairgun again but cannot recall how I get it to display the difference in size between mildots ie at 10x I know it should be 3.6" but if my maths is right as shown above I'm thinking it should be 4" at 100yds. Isn't there some way HFT shooters and others use the mildots to determine size of object? First though they woulkd surely have to be sure of the size between mildots at differing magnifications. I do appreciate that the mildot graphs show the different distances but it's not quite what I am looking for.
    Dag
     
  5. cloverleaf

    cloverleaf Honorary Member

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    In theory, assuming the rets of both 'scopes give true mil divisions on 10x, on 9x one division should be 1x(10/9)=1.11 mils - so yes, at 100yds this would be around 4".

    'scopes can vary though so it pays to put a ruler out at a known range and measure the displacement to get a proper idea.
     
  6. terry1001

    terry1001 Major Poster

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    Agreed, the markings on scopes are not accurate so the only way to be certain is to try it out on the range.
    When mil dots are used to measure the range you need to know the exact size of the target since if you're 10% out on target size then you'll also be 10% out on your range calculation. If you try and use them to work out how far away a rabbit is for example then how do you know the size of the rabbit?
    To get the best out of any scope ranging reticle it really needs to be used at a single (or fixed) magnification unless you have the time and patience to sit and work out a set of calculations before taking the shot.
    In Chairgun if you set up your details - rifle muzzle velocity, pellet, zero range, scope height and magnification - and select the appropriate reticle you can then turn on the scope cap or reticle view and you will see the range corresponding to each mark on the reticle. If you then alter the magnification you will see these values change and you can print off the images as well if you want to.
     
  7. imorik

    imorik Busy Member

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    http://www.bfto.org.uk/hfthints.htm

    Scroll down to the bottom of the page. Some rangefinding targets with mil dot ret printed on them. Simply print out one with a range you can use in the space you have and check to see if you have true mil dot at 9x mag.
     
  8. Dag

    Dag Pro Poster

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    Many thanks for all your replies. First off , at least I know my maths was correct ( for any US readers that's math to you folks! ;)) so I can easily calculate the height per mildot for any magnification albeit I do take the point about sticking with one mag level. This was easily done with the 4-16x scope as it had an adjustable objective lens but with the 3-9x I have to adjust the mag level to bring the target into focus at different distances. I think a change of scope is approaching!
    The point about knowing your targets height is well taken as is the need to check the accuracy of the scope settings on the range.
    Thanks again!
    atb Dag
    ps nice link imorik, ta!
    pps I've just read through some of the article and realise how little I know about range finding. Excellent info in it !
     
    Last edited: Aug 24, 2014

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