Wind deflection is non- deterministic element and is the most difficult challenge for all types of long-range shooting.
Wind is air in motion; a fluid. Fluids have a nasty habit of being chaotic and difficult to predict in general.
Wind is not a constant textbook 10 mph crosswind, but a real world wind complete with velocity gradient, direction changes, eddies, pick-ups, let-offs, vertical components, etc.
Since you can’t reliably measure and account for wind deflection, the best you can do is minimize its uncertainty and it effects. This is the best technical approach to dealing with the wind problem. There are two major things you can do to minimize the effects of wind: Practice reading your wind skills; by observing the cause and effect relationship between the wind conditions and bullet deflection. If you can obtain a real insight of how wind deflection works, you can make smart decisions about your equipment (rifle/bullet) that result in superior ballistics in the form of minimal wind deflection.
With a right hand twist rifle: Wind from the left will deflect a bullet to the right and down. Wind form the right will deflect a bullet to the left and up.
Wind Gradient: Wind gradient refers to the tendency for air currents to move more swiftly farther off the ground. Even on a windy day, when you get right down in the dirt and weeds, there is essentially no wind. However, if you were to sample the wind 10 feet above the ground, you would find an even higher wind speed. Depending on the terrain, the wind may reach full speed at high or low altitude. In general, the smoother the ground is, (i.e.) a frozen lake or flat desert, the less altitude is required for the wind to develop its full velocity. On the contrary, if the ground is covered with this weeds, grass, shrubs, trees, etc, the wind may not reach full speed until a much higher altitude. As the bullet arcs along it’s trajectory toward a distant target, it will rise, 10,15, even 20 feet above the ground and sometimes more than that if the shot goes over the valley. In that case, the bullet can be flying thru a wind speed that’s far greater than the shooter is able to sample from his position, or observe on the ground near the targets’ location.
Beating the wind:
Wind deflection is the most influential non-deterministic element in long range ballistics.
The best strategy for beating the uncertainty of wind deflection is to minimize its uncertainty and its effects.
Lag time is the fundamental measure of merit for wind deflection. Lag time is reduced by using high BC bullets and high muzzle velocity.
In a trade – off between low BC ( light weight) bullets at high speed compared to high BC ( heavy) bullets at reduced speed, the high BC bullets at lower speed will produce less lag time and wind deflection.
The academic debate between near wind and far wind is trumped by the unique realities of wind pattern to each specific range. The best policy for shooting in the wind is flexibility and critical assessment of the features unique to each range.
Wind does not blow on the side of the bullet to cause deflection. Instead, the bullet weather vanes into the oncoming airflow. A crosswind will make the bullet fly at a small angle to the line of sight. The aerodynamic drag applied to the bullet acts directly back along the bullet axis, which effectively pulls it away from the line of sight.
Wind gradient is when the wind velocity increases with increased height above the ground. It can be difficult to judge the wind speed high above the ground when shooting over valleys where there are no indicators, but you can usually count on higher velocity winds in such cases.
Cross wind weighting factors can be used to calculate the effects of multiple winds. The most wind sensitive portion of a bullet’s trajectory is not always the first segment. If the bullet will go transonic during its flight, that will dictate where the bullet is most sensitive.
Aerodynamic jump is a mechanism by which a bullet can have a vertical deflection when fired into a purely horizontal crosswind speed. This deflection is a constant angular deflection, roughly equal to .03 to .04 moa per mph of crosswind speed, and it depends on the gyroscopic stability of the bullet at the muzzle. The deflection is down for a left – right crosswind, and up for a right to left crosswind. These directions are reversed for a left twist barrel.
Point forward flight means that the nose of the bullet is always pointed straight into the oncoming air flow like a weather vane. Now the axis of the bullet is no longer aligned with the line of sight. Arrows are stabilized with fetching, and bullets are stabilized with spin, the both point their nose into the oncoming air flow when they are stable in flight.
For a given range and atmospheric condition, lag time and wind deflection depend on muzzle velocity and BC.
In general, a headwind will cause a bullet to slowdown faster and strike the target lower and vice versa for a tail wind.
