GIGO: Why Your Ballistic Calculator is Inaccurate

Sendit Ballistics, my own calculator, has a great reputation for accuracy. My algorithm takes a lot into consideration, and this results in excellent performance for medium to long range shots. However, the truth is that most all ballistic calculators will give reasonably good data.

While calculating trajectories in compressible flow (bullets flying quickly through air) requires advanced mathematics, it’s a fairly mature field. The reason your calculator gives you bad data probably has nothing to do with the calculator’s algorithm. Rather, it is a phenomenon known as GIGO: Garbage In, Garbage Out.

Your ballistic calculator relies on the following data, in order from the most important to least important:

  1. Ballistic Coefficient – This is generally a “G1” or “G7” class coefficient. All it means is that the bullet is benchmarked against a standard shaped object, and its performance is measured relative to that well known drag profile. You can get real nonsense if you input a G1 BC in place of a  G7 BC.
  2. Muzzle Velocity – Get this too wrong, and your range card will be useless past 500 meters.
  3. Weight – Inputing the wrong weight will make your bullet seem to perform better if it is too heavy, or worse if it is too light.
  4. Zero range – If you input the wrong zero range, by a large margin, you can easily get unhelpful corrections.

Less important: scope height, weather, twist rate, Coriolis effect.

Happy hunting.