Range Report  Drag coefficient changing with velocity

flyfisherman246

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May 26, 2017
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I have searched high and low and can't find a good explanation on why the drag coefficient of a bullet gets higher as velocity slows before it hits transonic. What is causing the bullet to have less drag at higher velocities?
 

CoryT

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  • Mar 5, 2004
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    It relates to the position of the shock wave and the change in flow at the base. Base drag is quite significant, which is why we have boat tails. If you look at spark photographs that show the air flow around the bullet, you can see the change in position of the bow wave, the changes in the boundary layer flow and the increase in base drag as the projectile slows down.

    Bullet Shockwaves in SloMo
     

    flyfisherman246

    Private
    PX Member
    Minuteman
    May 26, 2017
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    It relates to the position of the shock wave and the change in flow at the base. Base drag is quite significant, which is why we have boat tails. If you look at spark photographs that show the air flow around the bullet, you can see the change in position of the bow wave, the changes in the boundary layer flow and the increase in base drag as the projectile slows down.

    Bullet Shockwaves in SloMo
    Dude!!! That is so awesome and makes so much sense. Thank you so much for posting that.
     

    flyfisherman246

    Private
    PX Member
    Minuteman
    May 26, 2017
    444
    130
    It relates to the position of the shock wave and the change in flow at the base. Base drag is quite significant, which is why we have boat tails. If you look at spark photographs that show the air flow around the bullet, you can see the change in position of the bow wave, the changes in the boundary layer flow and the increase in base drag as the projectile slows down.

    Bullet Shockwaves in SloMo
    So I see what you are saying here, and this makes sense. What about the added drag of the increasing yaw angles at longer ranges. I'm guessing this has something to do with it as well?