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Inclined Fire, part #3.1: NDS, or the fall of the favorite

I started with NDS method first because their other methodologies seem to be simple,
straightforward, and highly applicable. I consider their sniper/DMR training and Perotti's
book on sniping top of the line.

In that book, "From 1 to 1,000", inclined fire is covered by a couple of paragraphs that say approximately the following:

1. No correction within 160 MIL (≃9.1º).
2. For larger inclinations
2.1. Calculate difference in altitude between shooter and target, either using a map or by multiplying the distance by sine of inclination angle;
2.2. Divide by 3
2.3. Subtract this number from linear distance to the target, resulting in "equivalent horizontal distance" (EHD).
2.4. Take adjustments as if shooting horizontally at EHD.

Item 1 is clear. Item 2 can be rephrased as EHD = D - D * sin(α) / 3, where D is distance to target and α is absolute inclination.

JBM and LO-Calc gave surprising results (I did not believe it at first, had to check twice):

GP11 vertical miss distance, cm


15 20 25 30 35 40 45 50
300 -9.1 -10.5 -11.3 -11.3 -10.1 -8.1 -4.9 0.3
400 -19.9 -23.5 -25.4 -26.6 -25.3 -22.8 -17.4 -9.3
500 -35.4 -42.6 -47.0 -49.4 -49.8 -46.0 -39.2 -27.5
600 -58.4 -69.7 -79.3 -83.5 -84.7 -81.3 -71.0 -55.2
700 -88.7 -108.7 -122.8 -131.3 -133.9 -130.0 -118.7 -98.5
800 -131.7 -159.8 -182.1 -194.7 -201.2 -197.4 -185.8 -158.1
900 -189.2 -230.7 -261.5 -282.0 -292.3 -291.5 -275.8 -244.4
1000 -262.6 -321.8 -367.0 -398.7 -414.2 -415.5 -391.6 -360.6










-15 -20 -25 -30 -35 -40 -45 -50
300 -9.0 -10.3 -10.9 -11.1 -9.8 -7.8 -4.5 0.6
400 -19.5 -23.0 -24.7 -25.9 -24.4 -21.9 -16.4 -8.2
500 -34.5 -41.4 -45.6 -47.8 -48.0 -43.9 -36.9 -25.4
600 -56.8 -67.6 -76.7 -80.5 -81.3 -77.5 -66.9 -51.0
700 -86.0 -105.1 -118.5 -126.1 -128.1 -123.6 -111.7 -91.0
800 -127.3 -154.1 -175.1 -186.4 -191.9 -186.9 -174.7 -146.1
900 -182.7 -222.1 -250.8 -269.5 -278.0 -275.7 -258.5 -226.0
1000 -252.9 -309.0 -351.2 -380.1 -393.1 -392.0 -366.0 -333.2

Looks pretty much useless. Even simply fixing sights at 350 m works better.

Accuracy: bad
Domain: up to ≃400-500 m
Complexity: moderate -- 1 table lookup, 2 mathematical operations
Pros: none
Cons: inelegant and useless

How this method made its way into otherwise excellent book is beyond my comprehension.
Looks like nobody's perfect.

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Article | by Dr. Radut