Why distance matters so much
Bullet drop is a roughly parabolic function of distance. At 100 yards a .308 Win may drop 1–2 inches from a 100yd zero. At 500 yards that same round may drop 50+ inches. A 10% ranging error at 500 yards means a miss — the bullet impacts 5+ inches from your aim point.
Wind drift compounds the problem: wind drift scales approximately with time-of-flight squared, and time-of-flight scales with distance. Getting distance right is foundational to every other correction you make.
Laser rangefinder
A quality laser rangefinder (LRF) is the gold standard. Modern units are accurate to ±1 yard out to 1000+ yards. Best practices: range multiple times and confirm consistent readings, range off the base of the target (harder surface returns stronger signal), and range before conditions change.
Battery failure, thick vegetation, and heavy rain can defeat an LRF. Always know your backup method.
Mil-ranging
Mil-ranging uses the reticle to measure the angular size of a known object, then calculates distance. The formula: Distance (meters) = Object size (meters) × 1000 ÷ Mils measured.
For a standard human torso (~0.5m): if it subtends 1.2 MIL through the scope, distance = 0.5 × 1000 ÷ 1.2 = 417 meters. For a vehicle (~2.3m tall): subtends 3.1 MIL → 2.3 × 1000 ÷ 3.1 = 742 meters.
Accuracy depends on how well you know the object's actual size. Common known sizes: steel IPSC target (0.45m × 0.60m), standard door height (2.0m), truck height (~1.8m), military vehicle (~2.5m).
Practice mil-ranging at known distances until it's fast. The skill degrades without use.
Going deeper: the Sniper Skillset track's 'Range Estimation Without a Laser' lesson takes this further — a target-size library to memorize, the MOA version of the formula, and the bracketing and averaging methods that beat a single measurement.
Backup methods
Map/GPS: if terrain maps are available, GPS coordinates of your position and the target allow accurate distance computation. Takes time but is highly accurate.
Pacing: measure your stride (most adults, ~2.5 feet per pace). Walk between points and multiply by stride. Useful for short distances (<300m).
Subtension of terrain features: a known terrain object (the height of a specific building, a standard fence post at 1.8m) can substitute for a human target.
Bracketing: use DOPE data in reverse — if you can observe bullet impact trace and adjust until hitting, you can infer distance from the correction applied. Only valid if you have DOPE data for that rifle/load combination.