Wind and Weather

• Gravity• Drag• Temperature• Wind

Factors that affect trajectory

• Constantly applies a pulling force on the projectile that will eventually pull it to the ground.

Gravity

• The atmospheric resistance to a projectile moving through the air.

• Measured by the bullet’s ballistic Coefficient (B.C.)

Drag

• Affects the elevation setting required to hit the center of the target.

• A 20 degree Fahrenheit change in temperature affects the muzzle velocity approximately 50 fps

• Higher temperature = more velocity

• Lower temperature = less velocity

Temperature

• 1 minute adjustment for every 20 degree temperature change.

• Drop in temperature, raise elevation

• Increase in temperature, lower elevation

Temperature

• Wind has the greatest effect on ballistic trajectories.

• The amount of effect depends on:• The time the projectile is exposed to the wind• Direction the wind is blowing

• Velocity of the wind

• Will have the most effect on the projectile at the midrange point.

Wind

• 0-3 mph - Hardly felt, but smoke drifts

• 3-5 mph - Felt lightly on the face

• 5-8 mph - Keeps leaves in constant movement

• 8-12 mph - Raises dust and loose paper

• 12-15 mph - Causes small trees to sway

Wind estimation

Wind Formula

USAMU Service Rifle Section

Range(meters) X Velocity(MPH)

10

MOA of Drift=

5(00) meters X 5 MPH

10 = 2.5 MOA or 12.5”

Wind Formula Worksheet

Range(meters) X Velocity(MPH)10

= MOA of Drift

1) 300m @ 10mph (3mx10mph)/10= 3 MOA (9”)2) 500m @ 7mph3) 600m @ 15mph

5) 100m @ 15mph4) 400m @ 20mph

(5mx7mph)/10= 3.5 MOA (17.5”)(6mx15mph)/10= 9 MOA (54”)(4mx20mph)/10= 8 MOA (32”)(1mx15mph)/10= 1.5 MOA (1.5”)

400 m

8 mph

4(00) meters X 8 MPH

10

= 3.2 MOA or approx. 12”

Iron Sights

FrontSight

100m Hold-offs

3 MPH 5 MPH 10 MPH 15 MPH

200m Hold-offs

3 MPH 5 MPH 10 MPH 15 MPH

300m Hold-offs

3 MPH 5 MPH 10 MPH 15 MPH

• Preferred method of wind estimation is the use of optics to observe mirage

• Mirage is the reflection of light through layers of air that have a different temperature than the ground.

• These layers are blown by the wind and can be monitored to detect direction and speed

Mirage

• Focus optics on an object at the midway point, then look back to the target, or

• Focus optics on the target, then turn the focus knob 1/4 turn counterclockwise.

• Target will appear a little fuzzy, but mirage should be clear

• This will also aid the coach in reading the bullet trace

Mirage

Mirage

What are your questions?