Wind Deflection

            Wind deflection is another factor which has a great effect on a bullet. During wind deflection, gusts of air push the projectile and alter it from its original line of trajectory. A sudden gust of wind can change 50% in a matter of seconds and this causes the need for an adjustment. A shooter could deal with a 2-3 MPH winds and not feel a thing, or multiple crosswinds that are each traveling in different directions.

           A good technique to compensate for wind deflection is to first find out which direction the wind is blowing. This allows the shooter to determine how much "value" the current wind has. There is a simple clock-like diagram that you can use to find out the value. If you look at the diagram below you can see this diagram. Winds blowing from 2, 3, 4, 8, 9, and 10 o'clock are almost perpendicular to the shooter and will have the most effect on the bullet. These values need the largest adjustment. Winds coming from 1, 5, 7, and 11 o'clock are not fully perpendicular to the shooter so they are considered half-value, but still require an adjustment. Other winds are almost straight on and do not require adjustment. A lot of shooters then use vegetation around them or hand held wind devices to figure out how quickly that wind is moving.

         

           A formula for wind deflection is  D=W (T1-T2), where D is the deflection, W is the cross wind velocity in Feet per second, T1 is the time of flight for that range, and T2 is the range divided by the muzzle velocity.

          Imagine a 30-.06 round at 500 yards, or 1,500 feet. A 10-MPH wind moves at 14.76 fps and the muzzle velocity is ~2,800-3,000 fps, making the time of flight .744 seconds. If you run the formula, you find that the correction is 5.84 feet.