wind and weather. gravity drag temperature wind factors that affect trajectory
TRANSCRIPT
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?