How to Calculate Bullet Drop Speed & Wind Drag

The study of the physical and mechanical operations of projectiles, such as bullets, is generally called ballistics. There are three main things you can measure or predict regarding a bullet or other projectile. These are bullet drop, bullet speed, and wind drag. Bullet drop is the measure of the effect of gravity on the projectile. Speed is self-explanatory. Wind drag is the effect of the friction of wind on the speed of the projectile.

Things You'll Need

  • Firearm
  • Metal target
  • Measuring tape
  • Digital audio recorder
  • Computer
  • Audio editing software
  • Ballistics software
  • Web browser
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Instructions

  1. Bullet Speed

    • 1

      Set up a firearm and a metal target opposite the firearm at a distance sufficient to absorb the impact of the bullet. This distance will vary depending on the type of firearm.

    • 2

      Measure the distance from the firearm muzzle to the target. Note this number in feet (f).

    • 3

      Set up the digital audio recorder midway between the firearm and the target, and about ten feet away from the predicted bullet path. Set the recording volume at its lowest level and start recording.

    • 4

      Fire the firearm at the metal target.

    • 5

      Transfer the digital audio recording from the recorder to the computer and open the file in the audio-editing software.

    • 6

      Listen to the audio recording and note the points on the audio waveform where the gunshot happened and where the bullet hit the metal target. Measure the amount of time between the gunshot and the bullet impact. Note this number as a fraction of a second (s).

    • 7

      Calculate the speed of the bullet in feet per second (f/s). First, calculate the number of fractions of a second (s) in one second by dividing 1 by (s). Then multiply that number by the number (f). For example, if the distance between the firearm and the target is 300 feet and the amount of time it took for the bullet to get from the muzzle to the target was .1575 seconds, divide 1 by .1575 to get 6.3492. Multiply 6.3492 by 300 feet to get 1,904.76 feet per second.

    Bullet Drop

    • 8

      Measure the distance of the firearm muzzle from the ground as the number (d). For the sake of this example, we'll assume it is five feet.

    • 9

      Measure the time (t) it takes for a bullet dropped from a height of five feet to reach the ground. (t) equals the square root of distance (d) times two divided by the acceleration due to gravity (g). (g) is 32.152 ft/s2. In this example, at a height of five feet, time (t) will equal .558 seconds. The amount of time it takes a bullet to hit the ground doesn't change whether it has velocity or not.

    • 10

      Calculate distance (d) by multiplying time (t) as discovered in the previous step by velocity (v) as calculated in the previous section. In this example, (t) equals .558 seconds and (v) equals 1,904.76 feet per second. Therefore, bullet drop is 1,062.96 feet.

    Drag

    • 11

      Find an online or software-based calculator for determining drag. The actual calculations for determining drag are very complicated, requiring knowledge of calculus as well as multiple variables. Various websites and applications exist for this purpose, including the website for JBM Ballistics and most ammunition manufacturers.

    • 12

      Determine the variables. At a minimum, you will need to know the caliber of the bullet used, the wind speed, the distance to the target and the bullet velocity.

    • 13

      Input those variables into the website form or software and click calculate.