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  1. #1
    Member Puffin's Avatar
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    Differences between Trajectory Simulators

    Having run the same inputs for my long range load through the JBM Ballistics and Applied Ballistics online calculators, I've found a disconcertingly large difference between the two in predicted drop of around 200mm at a range of 800m and 350mm at a kilometre, equivalent to a difference of 50 ft/sec in muzzle velocity.

    Have you also come across differences like this between trajectory simulators, and if you have then what online or PC-based calculators (not apps please) have given the best match to observed drop and chronographed MV data for you please ?
    Last edited by Puffin; 15-05-2017 at 12:00 PM.

  2. #2
    Member Beavis's Avatar
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    Using the G7 model?

  3. #3
    Member Puffin's Avatar
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    Yes - 140grVLD so using G7. The Applied Ballistics calculator matches the observed drops (out as far as measured to date - which is 800m) for a muzzle velocity of 2900ft/sec that also matches my chronograph readings. On the other hand I have to back off the MV entered into the JBM to 2850 ft/sec to get the same trajectory output. For some reason the JBM appears to be treating the bullet as being a bit more slippery for its quoted BC than the AB calculator. I have Eotvos correction and other advanced features disabled so the comparison should be a fair one.
    I'd like to run the same data through some other calculators for further comparison, so if there are any recommendations out there...?

  4. #4
    Member Puffin's Avatar
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    OK, have now compared outputs from the Hornady 4DOF simulator with the other two and get a good match to the Applied Ballistics data. The following doc identifies the difference likely to be found between the Hornady & JBM as stemming from using a generic G7 model (JBM) rather than drag functions specific to each projectile (Hornady).

    http://www.hornady.com/assets/files/...l_Paper_V2.pdf

    The down side to the Hornady calculator is that there are currently only a limited number of projectile drag files in the Hornady library for non-Hornady bullets so I've used the Berger 140gr hybrid as an approximation to the VLD.
    For ELD users though these are all loaded and the trajectory predictions promise to be the most accurate available.

    Strange that the Hornady & Applied Ballistics data should match, as the AB is also a BC-based simulator, so questions remain....

 

 

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