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Thread: Help understanding the POI changes with altitude / range finding data / Leica HD-B

  1. #1
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    Help understanding the POI changes with altitude / range finding data / Leica HD-B

    Hey team,

    I'm trying to get a better understanding on the point of impact with differing altitudes when hunting. Some of my tahr hunting is around 700metres however i have shot a bull at 1800m. A lot of difference.

    I have a pair of Leica HD-B 3000 binos arriving in the next week or so. Apparently these give an MOA reading which will take into account the atmospheric pressure, angle etc.

    I am having a load developed on a new 7mm mag. Obviously the data gathered from this will be at a much lower altitude. Does this change anything? I can input this data into the HD-Bs.

    Basically I want to be able to point my Leica's at a target no matter the altitude and have an accurate MOA reading to input into my VX6HD.

    If possible I want to avoid using a smart phone to enter data(strelock) and I think I can achieve this by these new binos.

    Sorry if I'm a bit vague, hard to put into words!

    Cheers

  2. #2
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    I understand you avoiding strelock but download it and play around with different settings on it and it will give you an idea
    hotsoup likes this.

  3. #3
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    Does this change anything?

    No

    Not if the Binos do everything you say they will plus temperature.

    Your biggest enemy will always be wind, master that (or even half master it) and your winning.
    hotsoup and dirkvanvuuren like this.

  4. #4
    Member chainsaw's Avatar
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    For hunting purposes I create drop chart based on 3000 ft alt (typical bushline), 15C , 1010 hPa and 85% rel hum for average for "summer" conditions.
    If you change your alt by 1000 ft or so, it makes stuff all difference to your drops - well, not for normal hunting ranges anyway, out to 600 - 800 yards. Further out you need to pay more attention.
    For example with 7mmRM running 162 MAX @ 3000fps, then drop at 500 yards = 6.6 moa at 3000ft and 6.7moa at 300ft alt.
    At 800 yrds its 15.1 moa at 3000ft vs 15.6moa at 300ft. A 0.5 moa change with 2700ft alt difference. ( this is using the Hornady online ballistics app)
    Like @223nut says, you can use any of the on line ballistics packages to model out the impacts. Play around with all variables, not just alt - temp & air pressure etc, and you'll get a very good feel for the magnitude of impacts.
    Remember BC is the gift that keeps giving, high bc pills will be less affected
    hotsoup likes this.

  5. #5
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    I just plugged some numbers into Strelok for my 243 at 865m (coz that the last distance I shot it at). Adding 1000m altitude and dropping temperature 10 degrees (and using default pressure for that altitude) changed the elevation adjustment from 22.8 MOA to 22.3. So not much really.

    90gr ELD-X by the way, reasonable BC around 0.400
    hotsoup likes this.

  6. #6
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    Interesting, good feedback. Max I have ever needed/want to shoot out is 500/600. Maybe I'm overthinking it and there will be little to no difference with the ranges I shoot and the differing altitudes.

  7. #7
    Sending it Gibo's Avatar
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    I think pressure would be more useful than altitude. Could just make some drop charts up with various settings and have a little flippy book Then all you need from the rangies is TBR
    chainsaw likes this.

  8. #8
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    Yeah inside that range you will see more vertical variation from poor sd than from altitude, so that would be a primary consideration.

    However if you have the tools to measure it, when you are validating your drops at the range, taking a temp, humidity and barometric pressure is pretty easy and will ensure the baseline is accurate and the extrapolated data is good.

  9. #9
    Member Ryan_Songhurst's Avatar
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    You just put your load info in including the atmospheric pressure when the load was zeroed and the leicas will take that into account. Same with the 2700b rangefinder, I can't be bothered with it though so just use strelok on my phone and get tbr off the rangefinder
    hotsoup and dannyb like this.
    #30GANG....

  10. #10
    Member sneeze's Avatar
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    The only affect altitude has is by way of barometric pressure. If your system reads and calculates pressure then you can disregard altitude.
    hotsoup and Rock like this.
    Rules are for the obedience of fools
    and the guidance of wise men” Sir Douglas Bader.

  11. #11
    Member zimmer's Avatar
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    This is an article I have saved on my PC which I read every now and again when I forget the basics ( more and more frequently).

    https://bisonballistics.com/articles...cs-calculators

    If you don't want to read the whole article just jump to the end to "Practical Takeaways".
    It lists the best inputs for your ballistic calculator.

    I go with the first option (Direct Measurement) and just use the Link function from my Kestrel 5500 to my phone running Shooter.
    Yep, no need to worry about altitude, the ballistic program does the calculated effects of that internally.

    However for printed drop charts ie not carrying a Kestrel or similar, I have no experience and will leave it to others who have.
    Last edited by zimmer; 01-11-2019 at 05:15 PM.
    hotsoup likes this.

  12. #12
    Member zimmer's Avatar
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    Another reasonable article
    Long Range Shooter| Temperature Effects on Zero

    And if you want to get messy here’s one on calculating Density Altitude (why would you bother)
    https://www.weather.gov/epz/wxcalc_densityaltitude

 

 

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