Here's an article that I saved from a while back. It's by Long Gun Training LLC.
Wind outline from Long Gun Training LLC
Wind is a female, she needs to be figured out, caressed, softly talked too, pampered, squeezed and at times manhandled, but in the end, can still be a bitch.
Ballistic Analysis cause and effect
A shooter needs to understand measure and correct for the
magnitude of the crosswind component perpendicular to the bullets flight. To generalize how wind affects a bullet, it does not push the bullet off course; a crosswind makes the bullet yaw like a weather vane into the wind. A bullet’s drag force is in the direction directly to the rear of it while in flight. Once a yaw of the bullet takes place, this drag force now has a side force to it in relation to its flight path. So in essence, the bullet is actually pulled or sucked by the force vector of its drag during its yaw in flight.
The greater the crosswind, the greater the bullet yaw, the greater the drag force vector.
How to read and measure
How does one read it? For those who paid attention in physics and earth science class, wind is not a linear force but we do calculate it that way. (Example: Ever been in an open field of tall grass or grain on a windy day, look at the grass, it moves much like waves on the open sea moving back and forth, ebbing and flowing so to speak, varying in its strength and direction.) We try to input this into a linear force based on time of flight equation best we can.
Which wind zone matters most
The total range to a target is generally broken down into 3 zones; near the shooter (first 1/3), mid-range (second 1/3), and near the target (last 1/3). All wind zones matter for a quality solution in the end. Here are the percentages of influence.
For target ranges out to 500 yards the wind zone breakdown of influence on total bullet deflection is:
Near the shooter – 56%
Mid-range – 33%
Near the target – 12%
For target ranges between 500 yards and 1000 yards the wind zone breakdown of influence on total bullet deflection is:
Near the shooter – 44%
Mid-range – 39%
Near the target – 17%
Start Wind calls at your position
This is the foundation of all wind calls. It starts with you the shooter at the firing position. Depending on how much time you have, take several minutes and measure, average and evaluate the wind conditions at your position.
- It’s the only location you can “dope” the wind to within 1 mph.
- It’s where we are. When people talk about "feel" this is at the shooter.
- It’s where the highest percentage of influence on bullet deflection will occur.
(4) Steps of Judging Wind at your Position
- Judge how constant the wind is moving (constant vs gusts and let offs).
- Judge the direction at your position Direction is most commonly put onto a clock with 12 being the direction towards the target. 9 and 3 are considered to be full value in equations, 10:30, 1:30, 4:30 and 7:30 or quartering wind direction are referred to as half value (1/2) but in actuality are three quarter (3/4) of the wind velocity in equations.
- Judge the speed of the wind using a hand held wind meter like a Kestrel.
- Calculate a Solution using your ballistic program or formulas. Also keep separate data with real numbers of initial call and final call on this with target range and adjustment, to either reinforce or modify your personal wind calling tendencies (People’s wind calls are different from each other).
Doing these steps at your position, get used to coming up with a solution, then start judging changes in the wind conditions at your position.
This Judging changes is a key learning step. Once you think you have this figured out at your position. Then start the down range wind calls. There is more to this down range than you may first understand.
Down Range Wind Calls
Most that use "down range" calls have coaches, spotters or a lot of experience, and those coaches and spotters are watching the changes for you and relaying the data. You can't watch mid-range changes while you are focused on sending a round. It divides your attention. We can begin a call using mid-range but it can quickly change as wind is not constant.
Back to judging changes at your position…
Breaking down a total range into zones has value. As your experience grows, so does the distance down range where you can accurately call the wind depending on which indicators you may get. For a new shooter with little to no experience, again, you need to keep detailed accurate notes. As an example, if you say, "that is an 8 mph to 12 mph wind"- which is it - because a 1 mph wind at 1000 yards moves a 175 gr SMK 10". If you are 4 mph off in your call that is a
theoretical miss by 40". Knowing its 9 mph, would require you to actually “dope” it at your position. In order to build that personal database of experience, you have to keep notes and shoot. The better the notes, the quicker you'll be up to speed.
How to adjust sights to account for deflection
Taking a wind solution and adjusting your scope is done two ways. You can either dial the correction on the turret, or you can use your scale reticle to hold off for it. If there is a constant wind and you have time, dialing is a commonly used method. If you are hunting or in a tactical scenario where time is a factor, scale reticle hold off is preferred. One can also use both, in a changing wind scenario. The wind averages around 7 mph but gusts up to 12 mph and reduces down to 4 mph. Dial a solution for the 7 mph and use your scale reticle to adjust for your read of the changes in magnitude just before you fire.
Wind Gradient
As moving air (wind) gets higher away from ground terrain it tends to increase in velocity. A shooter must have an understanding of the trajectory of a bullet and gauge how high above the ground it will travel. Also, as a bullets travels up to the maximum ordinate of its ballistic arc and then back down, its time of flight is not whole in the maximum wind gradient. A generic increase of wind velocity per increase in altitude above the ground cannot be done without a study of the terrain and direction of the wind first.
