Cosines are useless for uphill/downhill

(If you click on the blue link, it takes you to the GunSim calculator, with the values filled in)

0 Degrees drop - GunSim (requires Java)

Drop at 700 yards, 0 degrees =  -228.25"

The Rifleman's "Cosine Rule" method says that at 45 degrees, 1000 yards is the same as 700 yards horizontal:

So instead of -228.25", we take the drop at 1000 yards, -672.94.

Let's try using a computer:

45 degrees drop - GunSim (requires Java)

Actual drop at 1000 yards, 45 degrees = -479.82

A 16 foot difference. Color me picky, but that isn't close enough for me.

You would be closer making no adjustment at all than using the rifleman's method in this case.


A. J. Pejsa "Modern Practical Ballistics" Ch 12: (The Rifleman's method) "To correct for the effect of an incline, they recommend imagining that the distance to the target is reduced to its 'horizontal component' ... This is the worst possible advice, and can cause serious errors in long-range shooting on steep inclines".

Too right.