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Tom's Ballistics

Detail info

Search calibers, enter rifle / ammo / atmosphere / target data, and compute a point-mass trajectory with G1–G8, GL, or a custom drag curve.

Units of measure Imperial Metric Default Imperial. Switching converts all form values and outputs.

Firearm & rifle data

Caliber / cartridge Optional · search 414 entries, or leave blank

Muzzle velocity (fps) Zero distance (yd) Scope height above bore (in) Twist rate (in/turn) e.g. 10 for 1:10 Twist direction RH drifts right · LH drifts left · flips aero jump

Sight / reticle Search iron, peep, magnified, red-dot, and holographic sights

Correction per click (in) POI shift per click at 100 yd Firearm weight (lb) Unloaded rifle / pistol weight for free recoil Powder charge (gr) Leave blank to estimate a typical factory charge

Bullet/ammunition specifications

Manufacturer / bullet lists show everything when caliber is blank; otherwise they filter by diameter (9,815 commercial bullets/loads). Choosing a bullet fills weight, length, BC, and drag model — you can overwrite any value. Measured lengths highlight green; typical caliber/weight averages fill without highlight.

Manufacturer All makers if caliber is blank; else filtered by diameter

Bullet / weight All bullets if caliber is blank; else by diameter / maker Bullet weight (gr) Overwritable Bullet diameter (in) Overwritable Bullet length (in) Overwritable

Drag model Standard reference projectile for the BC — shapes after common drag-model drawings

Ballistic coefficient Primary BC for the selected drag model, or scale factor for custom Cd Multi-band BC (optional) One line per band: fps, bc — use that BC at or above the airspeed (e.g. Litz multi-BC). Blank = single BC above. Sectional density SD = weight ÷ (7000 × diameter²) · lb/in²

Free recoil at muzzle (V0)

Recoil impulse —

Recoil velocity —

Recoil energy —

Enter firearm weight, muzzle velocity, and bullet weight to estimate free recoil.

Atmospheric environment

Atmosphere standard BC density reference · Apply fills sea-level T / P / RH

Temperature (°F) Barometric pressure (inHg) Leave standard sea-level P to derive from altitude Humidity (%) Altitude (ft) Density altitude (ft) From weather · override uses dry ICAO/ISA air (density + Mach) Use density altitude (ISA) Replaces T / P / RH with ICAO standard atmosphere at the DA above Override weather · switch to ICAO Latitude (deg) Optional · +N / −S · leave blank to skip Coriolis / Eötvös Azimuth / shooting direction (deg) Optional · 0° north · 90° east · both lat & az required for Coriolis

Target variables

Target distance (yd) Wind speed (mph) Wind direction (deg) 0° head · 90° right · 180° tail · 270° left Wind gust (± mph) Optional · shows ± windage band from gust on crosswind Wind profile (optional) Layered wind by range: range, speed, dir° per line. Blank = constant wind above. Example: 0, 10, 90 then 400, 14, 100. Shooting angle (deg) Positive = incline · negative = declination Table step (yd)

Stability uses the Miller twist rule as on the Berger Twist Rate Calculator (Sg₀ × velocity × atmosphere). Sg 1.5+ is preferred; 1.3 is marginal. Flat-base bullets are not well modeled. Windage includes aerodynamic drift, modified point-mass spin drift with McCoy spin decay (yaw-of-repose lift when Sg ≥ 1.3; RH drifts right, LH left — omitted when MPM assumptions break), Coriolis / Eötvös when both latitude and azimuth are entered, and Litz aerodynamic jump (vertical bias from crosswind; hand follows twist direction). Optional multi-band BC, range wind profile, and gust uncertainty improve long-range fidelity.