Jump to Navigation

Inclined Fire, part #2: When it doesn't matter

It's easy to google gory details on gyroscopic precession and Coriolis force and analyze every minute factor, but when (and if) is it worth doing?

Case study: standard army issue Fass 90 assault rifle, 300 m battle zero. How does it behave when shooting at an angle?

The Swiss army manual responds with exactly one concise sentence: "when shooting at an angle beyond ±30º, aim low". Not much for a mountainous country.

The table below shows nuances that the Swiss army manual glossed over. It contains drops in centimetres (the correct ones, already divided by cosine) for distances from 50 to 600 m and inclinations from -60 to +60 degrees.

Fass 90 + GP90, zero at 300 m


0 10 15 20 25 30 35 40 45 50 55 60
50 4.0 4.1 4.1 4.4 4.5 4.8 5.1 5.6 6.2 7.0 8.0 9.4
100 11.6 11.9 12.2 12.8 13.5 14.4 15.6 17.1 19.1 21.6 24.9 29.6
150 15.5 16.0 16.6 17.5 18.6 20.2 22.2 24.8 28.1 32.5 38.2 46.0
200 15.3 15.9 16.8 18.0 19.6 21.9 24.8 28.3 33.1 39.2 47.2 58.2
250 10.3 11.2 12.2 13.8 16.0 18.8 22.5 27.2 33.2 41.1 51.6 65.8
300 0.0 1.0 2.4 4.4 7.0 10.5 15.0 20.8 28.1 37.8 50.6 68.0
350 -16.3 -15.0 -13.5 -11.2 -8.1 -3.9 1.5 8.2 17.0 28.5 43.6 64.4
400 -39.4 -38.0 -36.1 -33.5 -29.9 -25.1 -18.9 -11.1 -1.0 12.3 29.8 53.8
450 -70.2 -68.6 -66.6 -63.5 -59.5 -54.0 -47.1 -38.1 -26.6 -11.7 8.2 35.4
500 -110.0 -108.2 -105.9 -102.6 -98.0 -91.9 -84.1 -74.1 -61.2 -44.5 -22.1 8.2
550 -160.0 -158.0 -155.5 -151.8 -146.6 -139.9 -131.4 -120.2 -106.1 -87.4 -62.9 -29.2
600 -221.8 -219.7 -216.9 -212.8 -207.2 -199.9 -190.4 -178.3 -162.6 -142.3 -115.4 -78.4














0 -10 -15 -20 -25 -30 -35 -40 -45 -50 -55 -60
50 4.0 4.1 4.1 4.4 4.5 4.8 5.2 5.7 6.4 7.2 8.2 9.6
100 11.6 11.9 12.3 12.8 13.5 14.4 15.6 17.2 19.1 21.8 25.1 29.8
150 15.5 16.0 16.7 17.6 18.8 20.3 22.3 24.9 28.3 32.7 38.4 46.2
200 15.3 15.9 16.8 18.1 19.8 21.9 24.8 28.5 33.2 39.4 47.4 58.4
250 10.3 11.2 12.3 13.9 16.1 18.9 22.6 27.4 33.4 41.4 51.8 66.0
300 0.0 1.1 2.5 4.5 7.2 10.6 15.1 20.9 28.4 38.0 50.9 68.4
350 -16.3 -15.0 -13.4 -11.1 -7.8 -3.7 1.7 8.5 17.3 28.8 43.9 64.6
400 -39.4 -37.9 -36.0 -33.3 -29.6 -24.8 -18.7 -10.7 -0.6 12.6 30.2 54.0
450 -70.2 -68.5 -66.4 -63.3 -59.1 -53.7 -46.6 -37.7 -26.2 -11.2 8.5 35.8
500 -110.0 -108.0 -105.7 -102.3 -97.5 -91.5 -83.6 -73.6 -60.7 -44.0 -21.8 8.4
550 -160.0 -157.8 -155.2 -151.3 -146.2 -139.5 -130.7 -119.7 -105.5 -87.0 -62.4 -29.0
600 -221.8 -219.4 -216.6 -212.4 -206.8 -199.3 -189.8 -177.8 -162.2 -141.9 -115.1 -78.4

From practical standpoint,

1. If the angle is small (< ±30º), shoot as usual.
2. If the angle is large, starting from 100 m aim at the pelvis.
3. If the angle is very large (> ±50º), starting from 100 m aim at the knees.

Up to 400 m (realistic maximum engagement distance for iron sights or low power optics) these rules of thumb work fine. That's probably what the army manual meant, but now we got the numbers behind the words.

Other assault rifles, e.g., АК74М, show very similar picture, and so does GP11 or .308.

English


Main menu 2

Article | by Dr. Radut