What is Atlas Ballistics?

Atlas Ballistics manages 2 data types including support articles. Helps you organize, track, and share your work in 1 place for teams and solo users.

What is the rifleman's rule?

On an angled shot you dial for the horizontal distance to the target, not the line-of-sight distance your rangefinder gave you. Multiply the slope range by the cosine of the angle and use that number. It works because gravity only acts vertically, so only the horizontal component of the flight path builds drop.

Does it matter whether I am shooting uphill or downhill?

For the cosine correction, no — a 30 degree slope needs the same correction up or down. There are small second-order differences at extreme angles and long range, but for field shooting the direction does not change the hold.

At what angle does this start to matter?

Under about 10 degrees you can usually ignore it. At 15 degrees you lose roughly 3 percent of the range, at 30 degrees about 13 percent, and at 45 degrees nearly 30 percent. Combine a steep angle with long range and the miss is measured in feet.

Is the cosine rule accurate at long range?

It is a very good approximation out to moderate distances and modest angles. Past roughly 700 yards or beyond 30 degrees it starts to drift because it ignores how air density and time of flight change along an inclined path. A full solver that integrates the actual slant path is better, which is what the Atlas app does.

How do I measure the angle in the field?

An angle-indicating rangefinder does it for you, and many give you the corrected range directly. Failing that, a scope-mounted angle cosine indicator or the inclinometer in your phone works. Guessing angles by eye is unreliable — most people overestimate steepness badly.

Features

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Free Ballistic Tool

Angle Shot Calculator

Steep uphill or downhill shot? Convert the range your rangefinder gave you into the true horizontal distance you should actually be dialling for.

The shot

Line-of-sight range

Angle (up or down)

Common angles

Uphill and downhill use the same correction. Enter the angle as a positive number either way.

Dial for

453.2yd

Use this as your range, not the rangefinder reading.

Cosine

0.906

What the angle costs you

Line-of-sight range500 yd

True horizontal range453.2 yd

Range removed46.8 yd

As a percentage9.4%

Elevation change634 ft

Correction chart at 500 yd

5°498.1 yd (−1.9)

10°492.4 yd (−7.6)

15°483.0 yd (−17.0)

20°469.8 yd (−30.2)

25°453.2 yd (−46.8)

30°433.0 yd (−67.0)

35°409.6 yd (−90.4)

45°353.6 yd (−146.4)

Why angled shots shoot high

Gravity pulls straight down, so it only has time to work on the bullet over the horizontal part of its journey. Point the rifle steeply up or down and a good chunk of the measured distance stops contributing to drop, which means the bullet needs less elevation than the raw range suggests.

Dial the line-of-sight number instead and you dial too much, so the shot goes high. Hunters run into this constantly in the mountains, where a 500 yard reading across a canyon at 30 degrees is really a 433 yard shot — a difference of well over a foot of impact for most cartridges.

The cosine rule handles field shooting well, but it is an approximation. It assumes the air and the time of flight behave as they would on a flat path, which stops being true at long range and steep angles. A solver that integrates the real inclined trajectory, including the altitude change along the way, is the honest answer at distance.

Get the full solver in your pocket

Atlas Ballistics runs this same engine on your phone — with wind, spin drift, Coriolis, aerodynamic jump, truing from real shots, saved rifle and ammo profiles, and range cards that work offline.

Download on the App Store

Free to start · No account required to calculate

Frequently asked questions

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Recoil Energy Calculator

Free recoil in foot-pounds for any load and rifle weight.

Angle Shot Calculator

Uphill and downhill range correction with the cosine rule.