Function quick_drop_estimate 

pub fn quick_drop_estimate(
    muzzle_velocity_fps: f64,
    distance_yards: f64,
    _bullet_mass_grains: f64,
    bc: f64,
) -> f64

Estimate bore-line drop for a horizontal shot in ICAO sea-level conditions.

Inputs are muzzle velocity in feet per second, distance in yards, bullet mass in grains, and a G1 ballistic coefficient; the returned drop is meters. Bullet mass is retained for API compatibility but does not enter the retardation calculation because G1 BC already includes the projectile’s sectional density and form factor.