BC: Our GA Drag Model/ Drag Coefficient

Forums Pellets, Projectiles, Slugs, & Ammo BC: Our GA Drag Model/ Drag Coefficient

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    JungleShooter
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    Member

    BC:  Our GA Drag Model/ Drag Coefficient

    There was some interest in the GA drag model for airgun pellets. This, together with a pellet's ballistic coefficient (BC), helps our ballistic calculators give us holdovers and holdoffs.

     

    I found the GA drag model:
    Strelok Pro has an option to enter custom drag profiles, and when going to that function the user can choose to "email" the data — and in reality it is a "share" option.

     

    The content of the text file (.txt) that Strelok gives me is listed below.

    The first number in each line is the drag coefficient (Cd), the second the mach number (though when entering this data in Strelok manually these are switched around).
     

     

    🌟   However, if I understand the pro ballisticians correctly, finding the custom drag model (CDM) for a projectile is much more accurate than one fixed BC with a one-fits-all drag model — mainly relevant for long-range shooting (100y and up).

     

    I'm planning to find the CDM for a couple of pellets in the next months (a bunch of pellets over a chrono at various ranges, don't have no LabRadar). 😊  Got any advice for me?

    Matthias

     

     

    CFM, GA, 0.0, 0.0, 0.00000, StrelokPro, 0.000, 0.000, 0.000, 0.0
    Chairgun GA retardation table for Diabolo Airgun Pellet
    0.250   0.000
    0.235   0.100
    0.221   0.200
    0.207   0.300
    0.196   0.400
    0.189   0.500
    0.189   0.600
    0.202   0.700
    0.241   0.800
    0.329   0.900
    0.488   1.000
    0.597   1.100
    0.649   1.200
    0.669   1.300
    0.672   1.400
    0.667   1.500
    0.657   1.600
    0.644   1.700
    0.630   1.800
    0.616   1.900
    0.602   2.000
    0.589   2.100
    0.577   2.200
    0.566   2.300
    0.556   2.400
    0.548   2.500
    0.540   2.600
    0.534   2.700
    0.529   2.800
    0.524   2.900
    0.521   3.000
    0.521   3.100
    0.517   3.200
    0.514   3.300
    0.510   3.400
    0.507   3.500
    0.503   3.600

    Mod Edit: moved to Pellets, Projectiles, Slugs and Ammo forum

    • This topic was modified 5 months ago by a Moderator.
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    ArmedLeftist
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    Hmmm…..I’m not quite sure how any Diablo pellet could have BCS like that. Should be around .03

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    JungleShooter
    Participant
    Member

    Those aren't the BC numbers (ballistic coefficients), but the drag coefficients. 😊

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    ArmedLeftist
    Participant
    Member

    Doh! My bad. Thanks!

     

    ive used Ballistic AE (ref my other post) for quite awhile with my powder-burners and hoped to able to get them to integrate the GA model since I am so used to their UI. Based on your post, I decided to try out StrelokPro Pro. Took me a bit to figure out how to configure it but, if the algorithms are correct, I think I’ll switch over to that app for air and powder. Thanks!

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    ArmedLeftist
    Participant
    Member

    JungleShooter

    BC:  Our GA Drag Model/ Drag Coefficient

    There was some interest in the GA drag model for airgun pellets. This, together with a pellet's ballistic coefficient (BC), helps our ballistic calculators give us holdovers and holdoffs.

     

    I found the GA drag model:
    Strelok Pro has an option to enter custom drag profiles, and when going to that function the user can choose to "email" the data — and in reality it is a "share" option.

     

    The content of the text file (.txt) that Strelok gives me is listed below.

    The first number in each line is the drag coefficient (Cd), the second the mach number (though when entering this data in Strelok manually these are switched around).
     

     

    🌟   However, if I understand the pro ballisticians correctly, finding the custom drag model (CDM) for a projectile is much more accurate than one fixed BC with a one-fits-all drag model — mainly relevant for long-range shooting (100y and up).

     

    I'm planning to find the CDM for a couple of pellets in the next months (a bunch of pellets over a chrono at various ranges, don't have no LabRadar). 😊  Got any advice for me?

    Matthias

     

     

    CFM, GA, 0.0, 0.0, 0.00000, StrelokPro, 0.000, 0.000, 0.000, 0.0
    Chairgun GA retardation table for Diabolo Airgun Pellet
    0.250   0.000
    0.235   0.100
    0.221   0.200
    0.207   0.300
    0.196   0.400
    0.189   0.500
    0.189   0.600
    0.202   0.700
    0.241   0.800
    0.329   0.900
    0.488   1.000
    0.597   1.100
    0.649   1.200
    0.669   1.300
    0.672   1.400
    0.667   1.500
    0.657   1.600
    0.644   1.700
    0.630   1.800
    0.616   1.900
    0.602   2.000
    0.589   2.100
    0.577   2.200
    0.566   2.300
    0.556   2.400
    0.548   2.500
    0.540   2.600
    0.534   2.700
    0.529   2.800
    0.524   2.900
    0.521   3.000
    0.521   3.100
    0.517   3.200
    0.514   3.300
    0.510   3.400
    0.507   3.500
    0.503   3.600

    Mod Edit: moved to Pellets, Projectiles, Slugs and Ammo forum

    I can’t quite tell simply by looking at the numbers but have you happened to evaluate to find out if the drag coefficients are linear between 0 and Mach 1.2? I suppose I could graph them but then…..work. 😉

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    ArmedLeftist
    Participant
    Member

    Re: “I'm planning to find the CDM for a couple of pellets in the next months”, do you think it would be helpful to work to the hundredths (maybe even thousandths) of Mach? At least for the velocities airguns work at?

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    JungleShooter
    Participant
    Member

    In the following post you'll find a graph, and also the person that can answer those questions…! Bob Sterne, aka rsterne.

    I'm just passing on what I've learned from him. As you can see from that post on GTA, I asked him first before I responded to your question about the GA drag function…! 😉

    Matthias

    Here's the link:

    https://www.gatewaytoairguns.org/GTA/index.php?topic=159961

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    ArmedLeftist
    Participant
    Member

    Cool, thanks!

     

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