CaliberAtlas › Methodology
How every number on CaliberAtlas is produced — the trajectory model, the specification sources, and the honest limits of each.
Accuracy first: where a value isn't reliably known, we leave it blank rather than invent one.
Case and cartridge dimensions and maximum pressures follow published SAAMI (United States) and CIP (Europe) standards. Wildcat and proprietary cartridges show gaps where no standard exists.
Trajectories come from a 2D point-mass integrator using the G1 drag function, with drag corrected for air density from temperature, altitude, barometric pressure, and humidity. The launch angle is solved numerically for your zero, wind drift uses the lag-time method, and inclined fire uses the rifleman's rule. Both drag models use the standard published reference tables (BRL/JBM G1 and G7) with a drag scale derived from the physics of standard air density — no fitted corrections — validated against manufacturer tables: across 8 factory loads from Federal, Hornady, Remington, and Winchester, predicted drop matches published tables within 0.31 MOA at every published distance and 0.11 MOA at 500 yards — see the accuracy page for the full comparison.
| Effect | Supported | Notes |
|---|---|---|
| Bullet drop | Yes | 2D point-mass, G1 drag |
| Wind drift | Yes | Lag-time method |
| Atmosphere | Yes | Temperature, altitude, pressure, humidity |
| Inclined fire | Yes | Rifleman's rule |
| Spin drift | Calculator only | When twist rate and bullet diameter are entered; not in the reference tables |
| Coriolis | Not in the public calculator | Latitude and firing-direction inputs are not currently exposed; do not treat public results as Coriolis-corrected |
| Aerodynamic jump | No | Not modeled |
| G7 drag model | Yes | Standard G7 table, used automatically when a load has a measured G7 BC; firing-test validated (see /accuracy) |
Unless overridden: 1.5-inch sight height, 59°F, 29.92 inHg, sea level, and 50% relative humidity.
Retained-energy references of about 1,000 ft-lb (deer-class) and 1,500 ft-lb (elk-class) are read directly from the trajectory table and never extrapolated beyond it.
The transonic zone (roughly Mach 0.9–1.2) is the model's weak regime: rimfire tables deviate up to ~0.5 MOA inside 100 yards, and centerfire predictions past the cartridge's supersonic range should be confirmed with measured dope. The G7 model runs only where a load carries a measured G7 BC (about 250 loads); all other loads compute under G1, and the stored per-cartridge reference tables are G1-computed. One representative load is shown per cartridge.
Ballistic calculator · Ballistic coefficient explained · Glossary