BallistaGuides · About
How we compute
Every number in a Ballista guide comes from one of two places: a trajectory solved for that article, or a published source named at the end of the article. We don’t round off someone else’s chart or repeat a number because it’s common on forums.
The solver
The worked examples are solved with the Ballista engine, the same ballistic core that runs inside the Ballista app. It’s a point-mass (3-DOF) trajectory model integrated step by step with fourth-order Runge–Kutta. It includes:
- standard drag functions G1, G7, G2, G5, G6, G8, GI, GS and RA4, with the bullet’s ballistic coefficient;
- air density from station pressure, temperature and humidity, including the speed of sound;
- wind from any direction, look angle (uphill and downhill) and cant;
- spin drift and the vertical jump from a crosswind, from twist rate and bullet length (Litz’s models);
- Coriolis and Eötvös effects when latitude and shot direction are given.
A point-mass model is what nearly every field ballistic calculator uses. It treats the bullet as a point that feels drag, gravity and wind, and adds spin effects from fitted models rather than simulating the bullet’s full rotation.
How the solver is checked
The engine ships with automated tests that run on every change:
- 20 reference trajectories solved by py-ballisticcalc, an independent open-source solver. Elevation and windage must agree within 0.1 mil to 800 yd and 0.2 mil beyond.
- 20 hard cases solved by a separate reference model written from first principles with a different integrator: 45° to 75° slopes, 10,000 ft altitude, subsonic and transonic loads, oblique winds, Coriolis at several latitudes, 10° of cant. These must agree within 0.01 mil.
- Printed ballistics tables from ammunition makers’ catalogs, reproduced from the published inputs.
The reference rifles
Two rifles run through most articles, so numbers can be compared between them. They’re the demonstration rifles in the Ballista app, so the app screenshots match the tables.
| 6.5 Creedmoor | .308 Winchester | |
|---|---|---|
| Bullet | 140 gr match, G7 0.326 | 175 gr match, G7 0.243 |
| Muzzle velocity | 2,710 fps | 2,600 fps |
| Sight height | 1.6 in | 1.75 in |
| Twist | 1:8 in, right | 1:10 in, right |
| Bullet length | 1.389 in | 1.240 in |
| Zero | 100 yd | 100 yd |
Unless an article says otherwise, the air is the standard sea-level atmosphere (59°F, 29.92 inHg, dry), the rifle was zeroed in that same air, and there’s no wind. Spin drift and crosswind jump are included.
Units
Distances are in yards, velocities in feet per second, drop and drift in inches. Angular corrections are given in MIL (milliradians) and MOA (minutes of angle, 1.047 in at 100 yd), because scopes come in both.
Corrections
If you find an error, write to info@ballistacalc.com with the article and the number. We’ll check it against the solver and the sources, fix it, and note the change.