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Terms & Definitions

A plain-English glossary of the words you'll meet sighting in and shooting at distance — grouped so you can find them fast.

Angles & adjustments

MOA — Minute of Angle

An angle equal to 1/60 of a degree. It covers about 1.047 inches at 100 yards (≈ “an inch per hundred yards”) and grows with distance. Most MOA turrets click in ¼ MOA.

MIL (Milliradian)

An angle equal to 1/1000 of a radian — 3.6 inches at 100 yards, or 10 cm at 100 m. Most MIL turrets click in 0.1 MIL. Also written “mrad.”

Click value

How far your point of impact moves per turret click — e.g. ¼ MOA or 0.1 MIL. AHL Sight converts a miss into the exact number of clicks.

Elevation

Vertical scope adjustment (up/down), the top turret. Used to dial for bullet drop.

Windage

Horizontal scope adjustment (left/right), the side turret. Used to dial for wind and spin drift.

Subtension

How much distance a reticle mark or one click of angle covers at a given range. One MIL subtends 3.6″ at 100 yd, 7.2″ at 200, and so on.

Holdover / hold

Aiming above (or into the wind of) the target using reticle marks instead of dialing the turrets. The opposite of “dialing.”

Ballistics

Muzzle velocity (MV)

How fast the bullet leaves the barrel, in feet per second (fps). Measured with a chronograph. The single biggest input to a trajectory.

Ballistic coefficient (BC)

A number describing how well a bullet resists air drag — higher means it holds velocity and bucks wind better. Given against a standard drag model (see G1/G7).

G1 & G7 drag models

Two standard bullet shapes BC is measured against. G1 suits flat-based bullets; G7 is more accurate for modern boat-tail match bullets at long range. AHL Sight supports both.

Trajectory

The curved path the bullet flies. Gravity pulls it down the whole way, so it always drops relative to the line of sight past the zero.

Bullet drop

How far below the line of sight the bullet is at a given range, usually in inches, MOA or MIL. The core of a DOPE table.

DOPE

“Data On Previous Engagements” — your table of come-ups (drop and wind) for each distance. AHL Sight builds one you can print.

Zero

The distance at which your line of sight and the bullet's path cross, so point of aim = point of impact. A 100-yard zero is common.

MPBR — Maximum Point-Blank Range

The farthest you can aim dead-on and still hit a target of a chosen size without holding over, by picking the zero that keeps the bullet inside that “vital zone.”

Muzzle energy

The bullet's kinetic energy as it leaves the barrel (½·mass·velocity²), in foot-pounds. A rough gauge of hitting power.

Wind drift

How far a crosswind pushes the bullet sideways by a given range. Higher-BC bullets drift less.

Spin drift

A small, steady sideways drift (usually to the right for right-hand twist) caused by the bullet's gyroscopic spin. Matters at long range.

Coriolis effect

A tiny deflection from the Earth's rotation that depends on your latitude and shooting direction. Only relevant at very long range.

Transonic

The speed band around the speed of sound (~Mach 1.2–0.8). Bullets can get unstable passing through it, so shooters like to stay supersonic to the target.

Sectional density (SD)

A bullet's weight relative to its diameter. Higher SD generally means deeper penetration and (with good shape) higher BC.

Twist rate

How fast the barrel's rifling spins the bullet, e.g. “1:8” = one turn in 8 inches. Faster twist stabilizes longer, heavier bullets.

Gyroscopic stability (Sg)

A number for how well the twist stabilizes a bullet. Below ~1.5 the bullet may not fly its best; AHL Sight flags low Sg.

Optics & reticle

Reticle

The aiming pattern in the scope — crosshair, dots or hash marks. A “tree” or mil-hash reticle has marks for holding drop and wind.

Parallax

Apparent movement of the reticle against the target when you shift your eye, caused by the target and reticle not being on the same focal plane. An adjustable-parallax scope removes it.

FFP / SFP

First Focal Plane: reticle marks stay true at every magnification. Second Focal Plane: marks are only true at one magnification (usually max).

Turret

The adjustment dials on the scope — elevation (top), windage (side), and often parallax/side-focus. “Dialing” means turning them to your DOPE.

Magnification

How much closer the scope makes the target appear, e.g. “4–16×.” The first numbers are the zoom range; the last is the objective lens size in mm.

Mil-dot

A reticle with dots spaced one MIL apart, used for ranging and holds. AHL Sight includes a reticle library (mil-dot, tree, MOA, BDC).

Setup & shooting

Sight height

The distance from the center of the bore to the center of the scope. It affects near-range trajectory and is a required input.

Point of aim / point of impact (POA / POI)

Where the reticle is pointed vs. where the bullet actually lands. Sighting in makes them match at your zero.

Group

The cluster of holes from several shots at one aim point. Its size (in inches or MOA) measures precision; its center vs. POA measures where to adjust.

True-up

Adjusting your muzzle velocity or BC in the calculator until its predicted drops match what your rifle actually does downrange. AHL Sight does this from a measured point.

Cold-bore shot

The first shot from a clean, cold barrel, which can land slightly apart from the rest — worth knowing for the first, most important shot.

Chronograph

A device that measures a bullet's muzzle velocity. Real chrono data makes a ballistic solution far more accurate than book values.

Cant

Tilting the rifle left or right. At distance even a small cant throws shots off, so a level is used to keep the scope vertical.

Powder-temperature sensitivity

How much muzzle velocity changes with ambient temperature (fps per °F). AHL Sight can correct MV for the day's temperature.

Educational reference. AHL Sight is a planning aid — always confirm your zero and dope with live fire and follow all firearm safety rules.