Where does the bullet library data come from?
The built-in entries are checked against manufacturer factory specifications. The larger downloadable library comes from an open-source community dataset.
Help & supportBob on Ballistics
Support.
Help with projectile data, trajectory modelling, G1/G7 drag, wind, spin drift, Coriolis, environmental inputs, truing, units and the results table.
10-page PDF guide
Download the guide
How Bob On Ballistics Works
A plain-English explanation of the physics behind the app, including gravity and drag, ballistic coefficient, zero and sight height, wind drift, spin drift, Coriolis, weather and altitude, truing, elevation trim, the transonic region and an appendix of the formulas used.
PDF • Can be viewed in-browser or saved for offline reference.
Common questions
Does the app work offline?
Yes. Ballistic calculations run on your device. An internet connection is only used if you choose to refresh the projectile library.
How do Imperial and Metric units work in Version 1.2?
Supported fields have their own unit control, so you can change them individually. All Imperial and All Metric buttons are provided as shortcuts, while the Results table keeps a single consistent result-unit system.
Why does the Calculate button stay at the bottom of the screen?
Version 1.2 uses a floating Calculate button so you can change inputs anywhere in the configuration and rerun the calculation without scrolling back to a fixed button.
How does inclination work?
Version 1.2 can include significant uphill or downhill shooting angles. You can enter the angle manually or use “Measure with phone” by holding the phone flat against the scope or rail, pointed in the same direction as the barrel. Leave the field blank for level ground.
What do the amber and red result bands mean?
Amber marks the transonic region where flight can become less predictable as the bullet approaches the speed of sound. Red marks subsonic flight after the transition.
Does the app share my location or any data?
No. Location, heading, altitude and pressure are used locally for calculations and are not sent to the developer. See the Privacy Policy for full details.