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 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 10mph(3mx10mph)/10= 3 MOA (9”) 7mph 15mph 15mph 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 Front Sight

100m Hold-offs 3 MPH5 MPH10 MPH15 MPH

200m Hold-offs 3 MPH5 MPH10 MPH15 MPH

300m Hold-offs 3 MPH5 MPH10 MPH15 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

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