Rifle Zero Calculator

Real bullets lose velocity to air drag continuously in flight, so the calculator uses an exponential decay approximation — velocity at distance equals muzzle velocity times e to the negative distance over a ballistic-coefficient-scaled factor — and numerically integrates that changing velocity over 20 steps to get time of flight. Assuming one constant average speed for the whole flight would understate time of flight and drop at longer distances, where the velocity has already dropped substantially.

A positive point-of-impact shift means the bullet's path is still above your line of sight at that distance — it hasn't fallen back to meet the sight line yet, which happens on the way out to and just past your zero distance. A negative shift means the bullet has already dropped below the line of sight, which is the normal case well past zero, and the size of the negative number is how far below your aim point the bullet is actually hitting.

It first computes how much the bullet would drop by your zero distance under gravity alone, then solves for the small upward tilt between the bore line and the sight line that makes the bullet's rising path exactly cancel that drop plus your sight height at that one distance. That same bore angle is then reused to project the bullet's path at any other target distance, which is how the calculator gets POI shift at ranges other than your zero.

The underlying model uses a simplified G1-style exponential drag curve and a flat-fire trajectory with no wind drift or Coriolis effect, and it doesn't know your actual bullet weight or true drag profile beyond the ballistic coefficient you enter. It gets you into the right neighborhood for come-ups, but a chronographed velocity and a proper ballistic solver (or verified range data) will always be more accurate for dialing a real scope at distance.