Glossary
Long-range shooting glossary
Short definitions, in one place. Where a term deserves more than a sentence, there is a link to the article that gives it one.
Trajectory and drag
| Term | Meaning |
|---|---|
| Ballistic coefficient (BC) | Sectional density divided by form factor: how well a bullet holds velocity compared with a reference projectile. Quoted in lb/in². See ballistic coefficient. |
| Drag model | The measured drag curve of a reference projectile, against which your BC is applied. See G1 vs G7. |
| G1 | Reference projectile with a flat base and short ogive. Suits round-nose, flat-base, pistol and most hunting bullets. |
| G7 | Reference projectile with a boat tail and long ogive. Suits modern match bullets, and its coefficient is far more stable across velocities. |
| Form factor | How your bullet's shape compares with the reference. Below 1 means it slips through the air better than the standard. |
| Sectional density | Bullet mass divided by the square of its diameter. Heavy for calibre means more momentum per unit of frontal area. |
| Lag time | The difference between actual time of flight and flight time in a vacuum. The quantity that drives wind drift. |
| Point-mass model | A solver that treats the bullet as a point with drag, integrating its path step by step. What this app uses. |
| Runge-Kutta 4 (RK4) | A numerical integration method — more accurate than simpler schemes at the same step size. |
| Time of flight (ToF) | How long the bullet takes to reach the target. Drives wind drift, spin drift and Coriolis alike. |
| Transonic | The region around the speed of sound, roughly Mach 0.9–1.2, where drag changes shape and predictions degrade. See transonic. |
Sights and corrections
| Term | Meaning |
|---|---|
| MOA | Minute of angle — one sixtieth of a degree. 1.047 inches at 100 yards, 2.91 cm at 100 m. See MOA vs MIL. |
| MIL / milliradian | One thousandth of a radian, subtending one thousandth of the distance: 10 cm at 100 m, 1 m at 1,000 m. |
| Click | One detent of a turret. Commonly ¼ MOA or 0.1 MIL — a fraction of a unit, not a unit itself. |
| Holdover | Aiming above the target instead of dialling, using the reticle's stadia. |
| Windage | The horizontal correction. In a solver's output it usually includes spin drift and Coriolis, not just wind. |
| Elevation | The vertical correction from your zero. |
| Zero | The distance at which the line of sight and the trajectory cross on the way down. See zeroing. |
| Scope height | Distance between the bore centreline and the scope tube centreline. See scope height. |
| Cant | Rotation of the rifle about the bore axis. Costs you horizontally in proportion to elevation dialled. See rifle cant. |
| FFP / SFP | First and second focal plane. FFP reticles subtend correctly at every magnification; SFP only at one, usually maximum. |
| Rifleman's rule | Multiplying slope distance by the cosine of the angle to get the distance gravity actually sees. See angled shots. |
Wind, air and drift
| Term | Meaning |
|---|---|
| Clock position | Shorthand for wind direction, naming the hour the wind comes FROM. 12 is a headwind, 3 is from your right. See reading wind. |
| Full value / half value | A crosswind at 3 or 9 o'clock is full value; at 1, 5, 7 or 11 it is roughly half. |
| Density altitude | The standard-atmosphere altitude at which air has the density yours currently has. Folds temperature, pressure and humidity into one figure. See density altitude. |
| Station pressure | The actual pressure where you are standing — what a solver needs. Not the sea-level-corrected figure from a forecast. |
| Mirage | Heat shimmer viewed through a spotting scope. The best wind indicator out along the flight path. |
| Spin drift | Sideways drift from the bullet's own rotation, following the direction of the rifling. See spin drift. |
| Coriolis | Deflection caused by the Earth's rotation during the bullet's flight. See Coriolis. |
| Eötvös effect | The vertical component of Coriolis: shooting east lands high, west lands low. |
| Stability factor (Sg) | How much gyroscopic stability the bullet has relative to what it needs. Below 1.0 is unstable; 1.4 and above is comfortable. |
Ammunition and data
| Term | Meaning |
|---|---|
| Muzzle velocity (MV) | Speed at the muzzle. The input a solver is most sensitive to. See muzzle velocity. |
| Standard deviation (SD) | How tightly a string of velocities clusters around its average. Needs at least ten shots to mean anything. |
| Extreme spread (ES) | Fastest minus slowest shot. Uses two data points and grows with sample size, which makes it a weak statistic. |
| Power factor | Bullet mass times velocity, used by dynamic disciplines to set a scoring class. |
| Grain (gr) | Unit of bullet mass. 15,432 grains to the kilogram; 7,000 to the pound. |
| Handload | Ammunition assembled by the shooter rather than a factory. |
| Lot | A production batch. A new lot can differ enough in velocity to need re-confirming. |
| DOPE | Data on previous engagements — corrections confirmed by shooting rather than calculated. See DOPE card. |
| Truing | Adjusting solver inputs until the prediction matches measured impacts. See truing. |
| Cold bore | The first shot from a cold, unfired barrel. See cold bore drill. |
Disciplines
| Term | Meaning |
|---|---|
| PRS | Precision Rifle Series — positional long-range competition, largely on steel at unknown or varied distances. |
| IPSC / USPSA | Dynamic practical shooting, scored on points divided by time. |
| Hit factor | Total points divided by stage time. See hit factor. |
| Stage | One scored course of fire within a match. |
| Positional shooting | Firing from anything other than prone — barricades, tripods, packs. See positional drill. |
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