Do you aim high or low when shooting uphill or downhill?

The geometry

Gravity is only paid for the flat part of the trip

Point a rifle up a 30-degree slope at something 500 yards out along your line of sight. That target is not 500 yards away on the map. It is 433 yards out and 250 yards up, and gravity pulls straight down the whole time, square across the flat leg of that triangle.

Split gravity into two pieces relative to your sight line and the whole thing falls out. One piece runs across the line of sight and bends the bullet away from where you are looking; that piece is gravity times the cosine of the angle, 87 percent of full gravity at 30 degrees. The other piece runs along the line of sight and only nudges the bullet's speed. Tilt the shot up or tilt it down and the cosine is the same either way, which is why both directions shoot high.

The numbers on that drawing are the engine's. Fired level, this .308 crosses 500 yards 61.5 inches below the line of sight. Tilt the same shot 30 degrees and it finishes 53.2 inches below instead. Your dope card does not know about the slope, so it still tells you to fix 61.5 inches of shortfall, and the extra 8 inches goes over the top of the animal.

How big is it, really

Steep or far. It takes one of the two.

Here is the honest version of the angle problem, which is less dramatic than the campfire version. Below is how far high the bullet lands when you range a target, dial the flat-ground dope for that distance, and shoot it on a slope anyway.

Inside 300 yards, anything under 15 degrees costs half an inch or less. That is smaller than your group, smaller than one click, and smaller than the error in your wind call. Most field shots live in that corner of the chart, which is why generations of hunters got away with never thinking about it.

The corner where it bites is steep plus far. At 30 degrees the miss is 2 inches at 300 yards, 8.2 inches at 500, and 20.3 inches at 700. Push it to 45 degrees at 700 and you are 44.3 inches high, very nearly four feet above the aim point. Sheep and goat country produces exactly these shots.

Angle-corrected range

The number your rangefinder quietly changed

The old field fix for all of this is the rifleman's rule: multiply the line-of-sight distance by the cosine of the angle and shoot the flat-ground dope for that shorter number. Most laser rangefinders with an inclinometer will do it for you and display the result, usually called angle-corrected range, horizontal equivalent range, or something similar. On our 30-degree shot the display would read 433 instead of 500.

That rule works, and it is genuinely useful when your dope lives on a printed card. It is also a little coarse, because drag does not scale with distance the way the cosine assumes. Look up 433 yards on a flat card and you dial 9.22 MOA where the exact answer is 10.16, which puts you about 5 inches low at 500 yards and roughly 12 inches low if you run the same shot out to 700. A solver that gets the true distance and the angle can do better, because it can compute the real time of flight first and only then apply the cosine.

So the rule of thumb is short: if the thing doing the math knows the angle, give it the real distance. If it does not, give it the corrected one. Trouble starts when you give it both.

The trap

Correct the angle twice and you shoot under it

Picture the sequence. Your rangefinder is in its angle-corrected mode, left there by a previous owner or by you last season, and it reads 433. You type 433 into your ballistic app. Then, being thorough, you also tell the app the shot is 30 degrees uphill. The app has no way to know that 433 is already a corrected number. It shortens the trip a second time. You dial 7.98 MOA on a shot that wanted 10.16 and the bullet goes under the animal.

Read the two failure modes against each other. Ignoring the angle costs 8.2 inches high. Correcting for it twice costs 11.4 inches low. Being too careful is worse than being careless here, and it is worse in the direction that produces a gut shot rather than a clean miss. The full spread between the two mistakes is 19.6 inches on a shot most people would call routine.

It scales the way you would fear. The double correction is a percentage of your whole come-up, not a fixed penalty, so it grows with the come-up.

At 700 yards and 30 degrees the doubled correction is 28.2 inches low. At 40 degrees it is 41.8 inches, which is more than three feet of error introduced entirely by doing the right thing one time too many. Nothing about the shot feels wrong while you are making it. The dope looks plausible, the angle is real, and the rangefinder was telling the truth about a distance you did not know it had already changed.

What to do

Three habits that end the whole problem

1. 1

   Find out which range your rangefinder is handing you.

   Range one target from a steep angle and read both modes if your unit has them. The angle-corrected number is always the smaller one. Then pick a mode and leave it there, because the failure only happens when you forget which one you are in.

2. 2

   Give the solver the slant range and the angle. Nothing else.

   One correction, applied by the thing that knows the time of flight. That is the 10.16 MOA row, the one that lands on the aim point. Never hand a solver a range that has already been shortened and an angle on top of it.

3. 3

   Under 15 degrees inside 300 yards, let it go.

   Half an inch. Spend the attention on your wind call instead, which is worth many times more at that distance. The angle earns its place in your process past 400 yards or past 20 degrees, not before.

How Wrist Dope handles it

One correction, and you never type the angle

Wrist Dope wants the true line-of-sight distance to your target and the look angle, and it applies the improved rifleman's rule exactly once: it solves the real trajectory at the real distance, then scales the result by the cosine. Every corrected number in this article came out of that same solver, the one that runs on the watch.

In practice that gives you exactly two correct setups. Pick one and commit to it, because they do not mix:

1. 1

   Straight range in, Wrist Dope measures the angle. The better way.

   Switch angle-corrected range OFF on your rangefinder and give the app the unmodified line-of-sight distance, always. The angle is not something you type: point the watch at the target and tap to lock, and the motion sensors capture the inclination with the heading. If your watch rides the rifle, the same Scope Level calibration that runs the Live Fire anti-cant level (a Pro feature) reads the bore's true inclination, so aiming the rifle at the target IS the measurement. The solver then applies its one correction, and it recomputes with the air every time conditions change.

2. 2

   Angle-corrected range in, no angle in the app.

   If you would rather leave your rangefinder in its angle-corrected mode, enter the corrected range it hands you and do not lock a target angle in Wrist Dope. With no angle locked the app applies no incline correction, so the rangefinder's one correction stands alone.

The one configuration that misses is the mix: an angle-corrected range AND a locked angle. That is the doubled bar in the chart above. If you use the level-mounted setup, checking that your rangefinder's angle mode is off is part of mounting the watch.