Tech Talk

Hunting season is upon us. Let's talk about different shooting conditions.

Shooting In The Rain

Many riflemen have noticed that bullets seem to impact higher on the target when fired under rainy conditions. Changes in humidity have little effect on the air density, and thus the flight of a bullet.

Changes in barometric pressure, on the other hand, do have an effect. In general, fair weather is accompanied by a high barometer, which means more air density and more resistance to the bullet. Likewise, rainy weather is likely to occur at times of low barometer, when air pressure is low, producing less air density and resistance to the bullet. A drop of 1" in the barometric reading will increase the ballistic coeffient by about 3 1/3%.

Another possible reason for high shooting on rainy days is decreased glare on the target, allowing a closer hold to the true aimpoint with post-type front sights.

Neither of these effects are of great interest for pistol or close in shots, but are important in long-range highpower rifle shooting.

Shooting Uphill Or Downhill

Most of us do all our range shooting on the straight and level, with muzzle and target placed at the same height. But shooting at mountain-dwelling game, like deer and sheep, may require shots to be taken at extreme angles, and these require some alteration of the aiming point.

Shooting is flatter since the force of gravity is applied at less than the usual 90 degree angle to the flight path. On a given slope, the effect is substantially the same in firing uphill or down.

To find the horizontal equivalent to a given slant range, the table below can be used, for elevations up to 45 degrees:

Slope In Degrees
(up or down)

0
5
10
15
20
25
30
35
40
45
Multiply Slant
Range By
1
.99
.98
.96
.94
.91
.87
.82
.77
.70

For example, the horizontal range corresponding to a slant range of 300 yards on a 45 degree slope is 210 yards. The rifle should be aimed for 210 yards; if aimed for 300, the bullet may pass over the target.

At small angles, the effect is trifling. At steep angles, however, it can become a major consideration, along with the difficulty of range estimation and angle determination in mountainous country.

And always keep in mind, if you're shooting down at the target, especially a large buck, do I really want to drag this sucker back up this ridge? Happy hunting.

Technical information was drawn from the NRA Firearms Fact Book
Tactical Arms Gunsmithing, Inc.
Huntsville, AL
256-651-6622

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