Inclined Shooting: Introduction

Introduction Shooting at an angle introduces another factor to a ballistic trajectory: gravity's subtle defiance. Contrary to a novice expectation, a shot at a target both above or below the shooter will always impact high. Inclined shooting matters because the angle of the shot affects the bullet's path due to the influence of gravity. When shooting uphill or downhill, the horizontal component of gravity's pull changes, causing the bullet trajectory to deviate from one shot level. This occurs because gravity acts perpendicular to the Earth's surface towards the centre, not simply 'into the ground', into, e.g., a mountainside. Therefore, a shot aimed high or low will have gravity ‘pull’ more on the velocity of the projectile (i.e. from the tip or tail of a bullet) rather than the path (i.e. down the side of the bullet). In effect, the bullet's trajectory will be shorter in the vertical plane, resulting in a higher point of impact. The magnitude of this This effect starts out subtle, but while you might intuitively ‘just hold up a little’ for small changes in angle at short to medium distances, you must employ more rigorous techniques for success at greater changes. variations. Rifleman's Rule, aka ‘Map Distance’ A first step to understanding the problem is to look at a simplified solution. The Rifleman's Rule states that any shot should be adjusted as if it was the purely horizontal distance to target - like a ruler on the map. What is the horizontal distance? It's the cosine of the incline multiplied by slant range. Given a target that is 500 metres away, but at a 20° incline, this distance is the slant range. It includes discounts the angle. angle, because it's line of sight. A laser rangefinder would show this value. So, horizontal distance: cos(20°) x 500 m = 469 m This difference can be significant, significant: here you might miss centre mass, so you better account for it. Problems with the Rifleman's Rule Out to 500 metres and below 20° inclination, the Rifleman's Rule will get you results. Not pinpoint accurate, but better than nothing. The further you shoot and the more you angle the gun, the more it breaks down. You'll still hit the vital zone at 500 m and 15°, but take it too out to 600 m and 20°, you will likely miss centre mass for the leg a shoulder instead. Alternative Solutions This FM and the follow-up guide present a method several times more accurate with only one additional step. With it, even out to 1000 m and 50°, you will make a centre mass shot look effortless.