# Found PhysicForums while working on ballistics problem

• Jim Hahn
Jim Hahn
How did you find PF?
Several different sites, including PhysicsForums, mention/discuss a formula for computing a bullet's Ballistic Coefficient based on measuring two downrange velocities where the measurements are made a distance L between them. This can be done with traditional skyscreen (optical) chronographs or doppler radar based chronographs, such as by Labradar or Garmin.

The formula is rather odd in that it involves a denominator with square roots of velocity. At first blush, how can we get rid of square roots of velocity?

BC = 0.0052834 * L /(sqrt(v1) - sqrt(v2))

I get annoyed when I see an equation like this because it leaves out so much. What are the units of L? Where did the magic number 0.00528 come from? What's the overall derivation? So I started work to answer my questions.

WWGD and berkeman
Welcome to PF, Jim. I see you've posted this in the technical forums as well, which should help you get good answers.

I'll also send you a Personal Message (PM) with some tips on how to use LaTeX to post math equations at PF.

Enjoy PF!

WWGD
Welcome to here.

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