Uphill, downhill, both shoot high

Shoot steeply uphill at a deer your rangefinder says is 500 yards away, dial for 500, and you will shoot over its back. Shoot steeply downhill at 500 and you will do exactly the same thing. Most people find the symmetry surprising, and it falls straight out of how gravity works on a projectile.

The geometry

Gravity acts straight down, always. It does not care which way your barrel points.

Bullet drop is a function of flight time and of gravity's pull perpendicular to the flight path. On an angled shot, only the horizontal component of the distance is subject to the full effect of gravity acting across the trajectory. The vertical component of the path contributes to line-of-sight distance without contributing proportionally to drop.

So the drop you actually experience corresponds to the horizontal distance, which is always shorter than the line-of-sight distance you measured. Dial for the longer number and you have dialled too much elevation. The round goes high.

Uphill or downhill makes no difference to this, because the horizontal component is the same either way. Small asymmetries do exist at extreme angles and long ranges, but for practical field shooting the effect is symmetric.

The rifleman's rule

The standard field correction:

horizontal distance = line-of-sight distance × cos(angle)

Range the target, measure the angle, multiply by the cosine, then dial for the result as if it were a flat shot.

When it actually matters

Two variables combine: angle and distance. Either alone is usually survivable; together they compound.

• Under about 200 yards at moderate angle: the correction is inside the vital zone of a big-game animal. Not worth thinking about.
• Past 300 yards at 15° or more: now it matters, and it grows quickly with both variables.
• Mountain hunting and canyon country: this is routine, not exceptional, and it is where most angle-related misses happen.
• Archery: far more sensitive than rifle shooting. An arrow flies slowly with a steeply curved trajectory, so a modest angle produces a large error. Angle compensation is close to mandatory for elevated stands and mountain terrain.

Where the simple rule breaks down

The rifleman's rule is an approximation. It treats the problem as pure geometry and ignores the fact that a bullet's drag and time of flight change along an inclined path in ways that don't scale perfectly with the cosine.

Within roughly 500 yards and moderate angles the error is small enough to ignore. At extended range, steep angles, or with slow heavy projectiles, the approximation drifts and it tends to over-correct. Refined methods exist that account for the changing air density and drag profile along the path, and a full ballistic solver that takes look angle as an input will do meaningfully better than the cosine multiplication.

What to buy and how to use it

• Any rangefinder sold for mountain hunting or archery should have an inclinometer. Confirm whether it displays line-of-sight distance, corrected horizontal distance, or both — you want to be able to see both, so you know what you are dialling.
• Understand what your unit is telling you. Some display a corrected distance, some display a holdover derived from a preset ballistic profile, and some display both. Feeding a corrected distance into a solver that also applies angle correction will double-correct and put you low.
• If you run a full solver, give it the angle, not a corrected range. Solvers that accept look angle handle the problem more accurately than the cosine rule.
• Practise on real terrain. Estimate the angle, then measure it. A few repetitions will calibrate your eye and show you how badly it was off.

FAQ

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