You guys with practical long distance shooting know far more than I do--but I'm going to go way out on a limb and throw some ideas out for the sake of discussion ; ).

If you consider a bullet's basic design--it is optimized to reduce friction--and lift induces friction (actually--it produces what's called "boundary layer separation"; in the case of a bullet the vortices produced by this separation "meet" at the trailing surface, just as they do off an aircraft's wing--a reason the popular boat-tail design helps reduce the effect of this trailing vortices). An aircraft flying through the air basically doesn't "see" a crosswind component as long as it's speed is greater than the velocity of the wind hitting it. In practical terms--the velocity of a bullet so vastly exceeds the speeds of random winds that it is virtually inconceivable that it could actually cause a bullet to go up or down as a result of the wind "hitting" the bullet surface. If this were true, than we would likely see instability in the bullet's flight--and the bullet would be "pushed" into yawing/tumbling.

Here is the somewhat "cosmic" part that's a bit hard to explain. Air itself can have tremendous mass when it moves in large areas. That is what I mean when I say the actual bullet trajectory changes little if at all as a result of wind velocity alone--it's the over-all "big box" of the ambient air parcel the bullet is traveling in that "moves" the bullet's path.

The area closest to the ground is the area that experiences the greatest friction of the wind upon the surface of the earth. This results in mechanical mixing of air-masses and to further complicate things the ground itself is convectively heating (heating by the sun). What you have is a pretty dynamic smorgasbord of airmasses doing all kinds of movement. In terms of a head or tailwind, I suspect the greatest effect on the bullet's path is not so much the direction/velocity of the wind as it is an increase or decrease in air density (drag).

Just food for thought!~ LOL