Wind Velocity

Before adjusting the sight to compensate for wind, the sniper must determine wind direction and velocity. He may use certain indicators to accomplish this. These are range flags, smoke, trees, grass, rain, and the sense of feel. However, the preferred method of determining wind direction and velocity is reading mirage (see paragraph d below). In most cases, wind direction can be determined simply by observing the indicators.

a. A common method of estimating the velocity of the wind during training is to watch the range flag (Figure 3-20). The sniper determines the angle between the flag and pole, in degrees, then divides by the constant number 4. The result gives the approximate velocity in miles per hour.

Flag Method
Figure 3-20. The Flag method.

b. If no flag is visible, the sniper holds a piece of paper, grass, cotton, or some otherlight material at shoulder level, then drops it. He then points directly at the spot where it lands and divides the angle between his body and arm by the constant number 4. This gives him the approximate wind velocity in miles per hour.

c. If these methods cannot be used, the following information is helpful in determining velocity. Winds under 3 miles per hour can barely be felt, although smo ke will drift. A3- to 5-mile-per-hourwind can barely be felt on the face. With a 5- to 8-mile-per-hour wind, the leaves in the trees are in constant motion, and with a 12- to 15-mile-per-hour wind, small trees begin to sway.

d. A mirage is a reflection of the heat through layers of air at different temperatures and density as seen on a warm day (Figure 3-21). With the telescope, the sniper can see a mirage as long as there is a difference in ground and air temperatures. Proper reading of the mirage enables the sniper to estimate wind speed and direction with a high degree of accuracy. The sniper uses the M49 observation telescope to read the mirage. Since the wind nearest to midrange has the greatest effect on the bullet, he tries to determine velocity at that point. He can do this in one of two ways:

(1) He focuses on an object at midrange, then places the scope back onto the target without readjusting the focus.

(2) He can also focus on the target, then back off the focus one-quarter turn counterclockwise. This makes the target appear fuzzy, but the mirage will be clear.

Reading Mirage Wind

e. As observed through the telescope, the mirage appears to move with the same velocity as the wind, except when blowing straight into or away from the scope. Then, the mirage gives the appearance of moving straight upward with no lateral movement. This is called a boiling mirage. A boiling mirage may also be seen when the wind is constantly changing direction. For example, a full-value wind blowing from 9 o'clock to 3 o'clock suddenly changes direction. The mirage will appear to stop moving from left to right and present a boiling appearance. When this occurs, the inexperienced observer directs the sniper to fire with the "0" wind. As the sniper fires, the wind begins blowing from 3 o'clock to 9 o'clock, causing the bullet to miss the target therefore, firing in a "boil" can hamper shot placement. Unless there is a no-value wind, the sniper must wait until the boil disappears. In general, changes in the velocity of the wind, up to about 12 miles per hour, can be readily determined by observing the mirage. Beyond that speed, the movement of the mirage is too fast for detection of minor changes.

3-14. CONVERSION OF WIND VELOCITY TO MINUTES OF ANGLE

All telescopic sights have windage adjustments that are graduated in minutes of angle or fractions thereof. A minute of angle is l/60th of a degree (Figure 3-22, page 3-34). This equals about 1 inch (1.145 inches) for every 100 meters.

EXAMPLE 1 MOA = 2 inches at 200 meters 1 MOA = 5 inches at 500 meters a. Snipers use minutes of angle (Figure 3-22, page 3-34) to determine and adjust the elevation and windage needed on the weapon's scope. After finding the wind direction and velocity in miles per hour, the sniper must then convert it into minutes of angle, using the wind formula as a rule of thumb only. The wind formula is—

RANGE (hundreds) divided by 100 VELOCITY (mph) = Minutes CONSTANT ^alue

The constant depends on the target's range.

RANGE (hundreds) divided by 100 VELOCITY (mph) = Minutes CONSTANT ^alue

The constant depends on the target's range.

Wind Meter For Sniper

If the target is 700 meters away and the wind velocity is 10 mph, the formula is—

7x10 = 5.38 minutes or 51/2 minutes

This determines the number of minutes for a full-value wind. For a half-value wind, the 5.38 would be divided in half.

Wind From Full Value

b. The observer makes his own adjustment estimations, then compares them to the wind conversion table, which can be a valuable training tool. He must not rely on this table; if it is lost, his ability to perform the mission could be severely hampered. Until the observer gains skill in estimating wind speed and computing sight changes, he may refer to Table 3-4.

RANQE (METERS)

WIND VALUE

3MPH MIN IN

SMPH MIN IN

7MPH MIN IN

10MPH MIN IN

200

HALF FULL

0.0 0.5

0.4 0.8

0.8 0.8

1.2

0.8 1.0

0.8 1.7

0.5 1.0

1.2 2.4

300

HALF FULL

0.5 0.5

0.9 1.7

0.8 1.0

1.3 2.7

0.8 1.0

1.9 3.8

1.0 1.5

2.7 5.4

400

HALF FULL

0.5 0.5

1.4 2.9

0.8 1.0

2.4 4.8

1.0 1.8

3.3 8.7

1.0 2.0

4.8 9.6

500

HALF FULL

0.5 1.0

2.3 4.5

0.8 1.5

7.8

1.0 2.0

8.3 10.5

2.5

7.5 15.0

600

HALF FULL

0.5 1.0

3.0 7.0

1.0 1.5

8.0 11.0

1.0 2.5

8.0 15.0

1.5 3.5

11.0 21.0

700

HALF FULL

0.5 1.0

4.0 9.0

'1.0 2.0

7.0 15.0

1.5 2.5

10.0 21.0

2.0 4.0

15.0 29.0

800

HALF FULL

0.5 1.5

6.0 11.0

1.0 2.0

10.0 19.0

3.0

13.0 27.0

2.0 4.5

19.0 38.0

900

HALF FULL

0.5 3.5

7.0 15.0

1.0 2.5

12.0 24.0

1.5 3.5

17.0 34.0

2.5 5.0

24.0 49.0

1000

HALF FULL

1.0 1.5

9.0 18.0

1.5 2.5

15.0 30.0

2.0 4.0

21.0 42.0

2.5 5.5

3.00 60.0

(METERS)

WIND VALUE

12MPH MIN IN

1SMPH MIN IN

18MPH MIN IN

20MPH MIN IN

200

HALF FULL

0.5 1.5

za

1.0 1.8

1.8 3.6

1.0 2.0

2.2 4.3

1.0 2.0

2.4 4.8

300

HALF FULL

1.0 2.0

3.3 6.5

1.0 2.5

8.1

1.5 3.0

4.9 9.8

1.5 3.5

10.9

400

HALF FULL

1.5 2.5

5.8 11.8

1.5 3.5

7.2 14.4

4.0

17.3

2.0 4.5

9.6 19.2

500

HALF FULL

1.5 3.5

9.0 18.0

ZO 4.0

11.3 22.6

5.0

13.8 27.0

2.5 5.5

15.0 30.0

600

HALF FULL

1.5 4.0

13.0 26.0

2.5 5.0

16.0 32.0

3.0 6.0

19.0 39.0

3.5 6.8

22.0 43.0

700

HALF FULL

2.5 4.5

18.0 38.0

3.0 6.0

22.0 44.0

3.3 7.0

26.0 83.0

4.0 7.8

29.0 59.0

800

HALF FULL

2.5 5.5

23.0 46.0

3.5 6.5

29.0 57.0

4.0 8.0

38.0 69.0

4.5 9.0

38.0 77.0

900

HALF FULL

3.0 6.0

29.0 56.0

3.5 7.5

36.0 73.0

97.0

5.0 10.0

49.0 97.0

1000

HALF FULL

3.5 8.5

36.0 72.0

4.0 8.0

48.0 80.0

5.0 10.0

54.0 103.0

5.5 11.5

60.0 120.0

Table 3-4. Wind conversion table.

Table 3-4. Wind conversion table.

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