D IRECTION AND V ELOCITY

1. To determine the wind direction and velocity, the sniper can use certain indicators, such as range flags, smoke, trees, grass, rain, and his sense of feel; however, the best way to determine wind direction and velocity is to read the mirage.

Indicators

1. A common method of estimating the velocity of the wind during training is to watch the range flag (Figure 4-22). To use this method, determine the angle between the flag and pole, and divide by 4. The result gives the approximate velocity in miles per hour.

Figure 4-22. Flag method.

1. If no flag is visible, hold a piece of paper, grass, cotton, or some other light material at shoulder level, and then drops it. Point directly at the spot where it lands, and divide the angle between your body and arm by 4. The result gives the approximate velocity in miles per hour.

1. If you cannot use the previous method, use the guidelines outlined in Table 4-10.

Table 4-10. Wind velocity and indicators.

VELOCITY INDICATOR

Under 3 miles per hour Barely felt, although it will make smoke drift 3 to 5 miles per hour Barely detectable on the face

5 to 8 miles per hour Leaves in trees move constantly 8 to 12 miles per hour Leaves and trash move 12 to 15 miles per hour Small trees sway

Mirage

1. Mirages can be observed mainly on days when the ground and air are different temperatures. A mirage is simply a reflection of heat through layers of air at different temperatures and densities (Figure 4-23).

Properly reading the mirage with a spotting telescope lets the sniper estimate wind speed and direction accurately for up to 12 miles per hour; winds beyond this speed cause the mirage to move too fast to detect minor changes.

1. Since the wind nearest midrange affects the bullet the most, the sniper tries to determine the velocity there. He can do this in one of two ways:

1. He focuses on an object from midrange, and then places the scope back onto the target without readjusting the focus.

1. He focuses on the target, and then backs off one-quarter turn counterclockwise. This makes the target appear fuzzy, but leaves the mirage clear.

1. As observed through the telescope, the mirage seems to move with the same velocity as the wind, except when the wind is blowing straight into or away from the scope. Then, the mirage seems to move straight up, with no lateral movement (a boiling mirage). The sniper might also see a boiling mirage when the wind is constantly changing direction.

NOTE: Firing during a boiling mirage can spoil shot placement; unless the wind has no value (speed), the sniper must wait until the boil disappears.

Figure 4-23. Types of mirages.

1. Barrel mirage is a condition that occurs when multiple successive rounds are fired allowing little time for the barrel to cool. This is most commonly occurs when firing semiautomatic or suppressed rifles, such as the M110 SASS. Heat escaping from the barrel is viewed as an additional mirage when viewed through the telescopic sight. There are two ways to reduce visible barrel mirage:

1. One method is to wrap the barrel or suppressor with either heat dissipating or insulating material.

1. Another is to reduce the magnification on the variable-powered scope.

NOTE: See FM 3-05.222 for more information about mirage.

Conversion of Wind Velocity to Minutes of Angle

1. All telescopic sights have windage adjustments that are graduated in MOA or fractions thereof. One MOA is 1/60th of a degree (Figure 4-24). This equals about 1 inch for every 100 yards (2.5 centimeters for every 100 meter).

1. Snipers use MOA to determine and adjust the elevation and windage on the weapon's scope. After finding the wind direction and velocity in miles per hour, the sniper converts them to MOA. He uses the wind formula as a guide only. He must remember that the range factor depends on the target's range. The wind formula is—

(Range/100) x Velocity = Minutes of angle (MOA)

Constant

The constant for M118 and M118LR is 10 at all ranges. Table 4-11 outlines the constant for all other rounds.

Table 4-11. Constant for wind formula.

RANGE (METERS) CONSTANT

100 to 500 15

600 14

700 to 800 13

900 12

1,000 11

Figure 4-24. Minutes of angle.

EXAMPLE

The target is 700 meters away and the wind velocity is 10 mph.

700 (Range)/100 x 10 (Velocity) = 5.38 (Minutes full-value wind) = 5.5 (Minutes full-value wind) 13 (Constant)

1. The observer estimates his adjustments, and then he compares them to the appropriate wind-conversion table (Table 4-12 for the M110 SASS or Table 4-13 for the M107 LRSR). The tables provide data on wind components and half and full values for ranges from 200 to 1,000 meters and winds from 3 to 20 mph. The table can be a valuable training tool for the sniper, but because he could lose it in a tactical situation, he should learn to estimate wind speed and compute sight changes without it.

Table 4-12. Wind-conversion table for the M110 SASS.

Table 4-13. Wind-conversion table for the M107 LRSR.

L

1. Light does not affect the trajectory of the bullet; however, it does affect the way the sniper sees the target through the scope. This effect can be compared to the refraction (bending) of light through a medium, such as a prism or a fish bowl. The same effect, although not as drastic, can be observed on a day with high humidity and with sunlight from high angles. The only way the sniper can adjust for this effect is to refer to past firing recorded in the sniper data book. He can then compare different light and humidity conditions and their effect on marksmanship.

1. Light may also affect firing on unknown distance ranges since it affects range determination capabilities.

T

1. Temperature affects the firer, ammunition, and density of the air. When ammunition sits in direct sunlight, the bum rate of powder is increased, resulting in greater muzzle velocity and higher impact.

1. The greatest effect is on the density of the air. As the temperature rises, the air density drops. Since there is less resistance, velocity increases and the point of impact rises. For example, if the sniper zeros at 50 degrees and fires at 90 degrees, the point of impact rises considerably.

1. The change in the point of impact is best determined by referencing past firing recorded in the sniper data book. As a rule of thumb, a 20-degree increase in temperature will raise the point of impact by one minute; conversely, a 20-degree decrease will drop the point of impact by one minute.

H

1. The sniper can encounter problems if drastic humidity changes occur in his AO. Altitude and temperature impact the humidity level. As the humidity rises, the point of impact goes down; as the humidity decreases, the point of impact goes up. As a rule of thumb, a 20-percent change will equal about one minute, affecting the point of impact. The change in the point of impact is best determined

by referencing past firing recorded in the sniper data book. The sniper should keep a good sniper data book during training and refer to his record.

SECTION IV. HOLDOFF

Certain situations, such as multiple targets at varying ranges and rapidly changing winds, prohibit proper windage and elevation adjustments. Therefore, the sniper should learn and practice elevation holdoff, mil hold, and windage holdoff techniques to prepare himself to meet these situations. Holdoff is a shift in the point of aim to achieve a desired point of impact.

ELEVATION

1. The sniper uses elevation holdoff to hit targets at ranges other than that for which the rifle is adjusted.

NOTE: This technique is used only when the sniper lacks time to reset the sight. He uses holdoff with the sniper scope only if several targets appear at various ranges, or he has no time to adjust the scope for each target.

1. When the sniper aims directly at a target at ranges greater than the set range, his bullet will hit below the point of aim. At lesser ranges, his bullet will hit higher than the point of aim. If the sniper knows this and understands trajectory and bullet drop, he can hit the target at ranges other than that for which the rifle is adjusted (Figure 4-25).

EXAMPLE

The sniper has adjusted the rifle for 500 meters, and a target appears at 600 meters.

The holdoff is 25 inches. That is, the sniper aims 25 inches above the target's center of mass to hit the target's center of mass. If another target appears at 400 meters, he aims 14 inches below the target's center of mass to hit it. Table 4-14 translates the amount of holdoff for sights set for 300 and 500 meters to points of aim on a body.

Figure 4-25. Trajectory chart.

1. When using elevation holdoff, the sniper can use the vertical stadia lines/hash marks on the DOS as aiming points (Figure 4-26).

EXAMPLE

The sniper must engage a target at 500 meters with the scope set to 400 meters. He places the first stadia line/hash mark 5 inches below the vertical line on the target's center of mass. This gives him a 15-inch holdoff at 500 meters (Table 4-14).

Figure 4-26. Elevation holdoff with the tactical milling reticle.

Table 4-14. Holdoff and points of aim.

SIGHT SETTING

(meters) TARGET RANGE (meters) POINT OF AIM

300 100 Waistline

200 Waistline

300 Center of chest

400 High chest

500 100 Top mil dot/stadia line

200 2nd mil dot/stadia line from the top 300 3rd mil dot/stadia line from the top 400 4th mil dot/stadia line from the top

500 Center of chest

600 1st mil dot/stadia line below crosshair

The sniper rarely achieves pinpoint accuracy when holding off, since a minor error in range determination or a lack of a precise aiming point might cause the bullet to miss the desired point.