An area that the deer hunter or shooter must be concerned about when shooting a rifle at longer distances is the fact that the bullet is going to rise and drop above and below the intended bullet path and that the wind will also blow the bullet left or right as the distance increases. The kill zone circle for a whitetail deer is approximately 6 inches therefore a skilled hunter can calculate using JBM Software the point where the bullet does not exceed 3 inches above or 3 inches below the bullseye. We call this Max Point Blank Range (MPBR). As an example my .243 Winchester bullet is a Sierra 100 grain Pro-Hunter spitzer that can be chosen from the first drop down menu on the screen which includes the Ballistic Coefficient already. I have chrono’d the bullet at 2820 fps and enter that as Muzzle Velocity.
At the bottom of the software screen are boxes that you can check such as Zero at MPBR so it is calculated automatically for you. The MPBR calculated is 272 yards but the wind at 10 mph at 90º and will blow the bullet off course by 7.5 inches. What do you do then? Your bullet will exceed the 3 inch radius and make a poor shot. Knowing the wind direction and practicing at knowing wind speed can help make this shot possible. If the wind is blowing from left to right you will hold to the left by an estimated 7 inches (an educated guess) at the 9 o’clock position thus the bullet will strike the center of the kill zone. Practice, Practice and Practice. If you have the opportunity to wait for the wind to momentarily subside then wait. Trees and leaves can tell you lots about the wind speed. Those who study wind say that if smoke or steam rises vertically wind is 0 to 1 mph; wind shows slight smoke or steam is 2-3 mph but not enough to move leaves; wind that is felt on your face and leaves rustle is 4 to 7 mph; leaves and twigs in constant motion and extends a light flag is 8 to 12 mph. If small branches are moving on trees then you are above 12 mph.
What is critical here is the angle of the wind as it relates to your shot. If the wind is blowing toward you or toward your target then the shot will likely be less affected by wind. It will be helpful to create a chart for your rifle that shows drop tables and wind deflection that you can tape to your rifle or carry with you in the field. Below is the resulting chart for the .243 Winchester demonstrating the wind effect at 275 yards is 7.5 inches otherwise the wind will push your MPBR to an adjusted 175 yard max shot based on a 10 mph wind where wind deflection is 2.9 inches.
Yes wind can really throw you off target so remember to practice. Other factors include bullet speed and energy below. For deer we need around 1000 ft-lbs and 2000 fps making the max shot here at 272 yards as well. Hope this helps! © 2015