Ballistics Guide for
Scope Reticles

The speed of the projectile as it leaves the barrel, measured in feet per second (fps) or metres per second (m/s). This is the single most important input — a 100fps error changes your 50-yard holdover by roughly 0.5 mil for an air rifle. Measure with a chronograph for best accuracy.

A number describing how efficiently a bullet retains velocity against air resistance. Higher BC = less drop and wind drift at long range. G1 BC is the common standard for hunting bullets (0.3–0.6 for most centrefire). G7 BC is more accurate for long, boat-tail bullets. For air rifles and short-range rimfire, BC is not needed — Reticle Plotter uses a simpler parabolic model.

The range at which your scope crosshair and bullet impact point align. All holdover marks are calculated relative to this distance. A 35-yard zero for .177 air rifle means the pellet crosses the line of sight at 35 yards; it will be higher than aim before that point and lower after. Getting your zero right is the foundation of all holdover work.

The vertical distance between the centre of your scope tube and the centre of your barrel. Typically 1.4–2.0 inches for most scope mounts. This affects near-zero accuracy significantly — the bullet and the scope sight line diverge from different starting heights. Measure with a ruler from barrel to scope centreline.

The angular unit used in mil-dot reticles. 1 mil = 1/1000 of a radian. At 100 yards, 1 mil subtends 3.6 inches. At 50 yards, 1 mil = 1.8 inches. The mil value of a holdover changes with distance — a 2-inch drop is 1.1 mil at 50 yards but only 0.56 mil at 100 yards. Reticle Plotter converts your actual inch drop to mils at each target distance automatically.

1 MOA = 1/60 of a degree = approximately 1 inch at 100 yards (1.047 inches precisely). Some scopes use MOA clicks and MOA reticles instead of mils. 1 mil = 3.44 MOA. Reticle Plotter currently works in mils; MOA reticle support is planned.

The distance above a target you must aim to compensate for bullet drop, so the bullet impacts where you aim. A holdover of 2 mil at 60 yards means: place the 2-mil mark on the target, and the bullet will hit the centre of the target. BDC = Bullet Drop Compensation.

A scope where the reticle scales with magnification — the mil values of the reticle remain accurate at all power settings. BDC holdovers calculated in Reticle Plotter work at any magnification on an FFP scope.

A scope where the reticle appears the same size at all magnifications but the image scales. The mil calibration is only accurate at one power setting — usually maximum. For SFP scopes, use Reticle Plotter at your scope's calibration magnification (usually max power).