Wind Drift Inconsistency
One aspect of wind drift that I have seen described two ways has to do with whether the wind "drifted" the bullet or it "turned" the bullet. Depending on the description the bullets in the following examples would land in two different spots, although subjected to the "same" amount of wind.
Shot #1: When fired at a target 500 yards away, there was a 20 mile per hour wind blowing from 9 o'clock to 3 c'clock, but only from the muzzle and for the FIRST 100 yards. then the air was still.
Shot #2: Also fired at a target 500 yards away and there was also a 2 mph wind blowing from 9 to 3, but it was only blowing at the 400 yard mark through the 500 yard mark. And for example purposes, let's say that this wind caused the bullet to drift 5 inches in that 100 yards.
Some writers describe wind drift as a movement of a bullet similar to a swimmer going across a moving river. the swimmer is pointed toward the shore so the affect of the current is to move the swimmer down stream only where it is pushing him. So in the two examples, both bullets faced the same 400 yards of still air and the same 100 yards of moving air, so regardless as to where the drift was located, both bullets had the same amount of drift and so both landed 5 inche3s to the right of the point of aim.
Other writers indicate that the wind actually changes the direction of the bullet. So the first bullet is turned some amount of degrees(minutes or seconds) from it's initial point of aim that in this case results in the bullet being 5 inches to the right, and when the wind is only occurring in the last 100 yards, the bullet has the same impact 5 inches to the right of point of aim. However when the wind is occurring at the muzzle and is blown off course 5 inches in the first 100 yards, since the course of the bullet has been changed, even though the wind has stopped, the bullet continues on it's new course, moving 5 inches to the right for each 100 yards travelled, resulting in landing 25 inches to the right at 500 yards.
While this second (changing the bullets course) description sounds reasonable, the problem is that what if the wind is blowing 20 mph 9 to 3 for the entire 500 yards. If the bullet's direction was changed by 5 inches in the first 100 yards, then it could be expected to change it another 5 inches for each additional 100 yards AND these changes would be additive to the course change of the bullet; so it would land 5 inches to the right at 100 yards, plus the initial change of 5 plus an additional change of 5 plus it's position at 100 yards, so at 200 yards it would land 15 inches to the right, or when it got to 500 yards would be something like 75 inches off point of aim, where as the non additive measurement would put the bullet landing a mere 25 inches from point of aim.
Thoughts?
Shot #1: When fired at a target 500 yards away, there was a 20 mile per hour wind blowing from 9 o'clock to 3 c'clock, but only from the muzzle and for the FIRST 100 yards. then the air was still.
Shot #2: Also fired at a target 500 yards away and there was also a 2 mph wind blowing from 9 to 3, but it was only blowing at the 400 yard mark through the 500 yard mark. And for example purposes, let's say that this wind caused the bullet to drift 5 inches in that 100 yards.
Some writers describe wind drift as a movement of a bullet similar to a swimmer going across a moving river. the swimmer is pointed toward the shore so the affect of the current is to move the swimmer down stream only where it is pushing him. So in the two examples, both bullets faced the same 400 yards of still air and the same 100 yards of moving air, so regardless as to where the drift was located, both bullets had the same amount of drift and so both landed 5 inche3s to the right of the point of aim.
Other writers indicate that the wind actually changes the direction of the bullet. So the first bullet is turned some amount of degrees(minutes or seconds) from it's initial point of aim that in this case results in the bullet being 5 inches to the right, and when the wind is only occurring in the last 100 yards, the bullet has the same impact 5 inches to the right of point of aim. However when the wind is occurring at the muzzle and is blown off course 5 inches in the first 100 yards, since the course of the bullet has been changed, even though the wind has stopped, the bullet continues on it's new course, moving 5 inches to the right for each 100 yards travelled, resulting in landing 25 inches to the right at 500 yards.
While this second (changing the bullets course) description sounds reasonable, the problem is that what if the wind is blowing 20 mph 9 to 3 for the entire 500 yards. If the bullet's direction was changed by 5 inches in the first 100 yards, then it could be expected to change it another 5 inches for each additional 100 yards AND these changes would be additive to the course change of the bullet; so it would land 5 inches to the right at 100 yards, plus the initial change of 5 plus an additional change of 5 plus it's position at 100 yards, so at 200 yards it would land 15 inches to the right, or when it got to 500 yards would be something like 75 inches off point of aim, where as the non additive measurement would put the bullet landing a mere 25 inches from point of aim.
Thoughts?
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My thoughts?
The wind doesn't "turn" the bullet as if you turned the steering wheel of a car. It "pushes" on the up wind side of the bullet and creates a slight vacuum on the downwind side of the bullet causing the bullet to "drift" laterally but on the same directional vector.0 -
A review of the NRA high power shooting record book should answer most of your questions on wind drift. There are tables for most popular long range cartridges. 0 -
First of all, it's wind deflection, not drift. A bullet will turn to follow the wind, not drift with it or be pushed by it. Once you understand and accept that simple principle of physics, it all becomes much clearer. Unfortunately, many shooters understand the principle but refuse to accept it.
Second, think of wind deflection in minutes of angle, not inches.
The wind nearest the muzzle is much more important that one near the target. Any deflection near the muzzle will still be present at the target (no matter how far away it is) unless something happens to change or reverse the deflection. In you first example, if the bullet is deflected 5 moa at 100 yards (5 inches), it will have the same 5 moa deflection at 500 yards (25 inches), or at 1000 yards (50 inches), or any other distance.
In your second example, the bullet is deflected 5 inches, but this time the deflection is at 500 yards, which is only 1 moa. So the deflection at 100 yards would be 0 moa, and at 1000 yards it would still be 1 moa (10 inches).
In your last example, the bullet is deflected 5 inches at 100 yards (5 moa) but it has turned to follow the wind, so if the wind is still present all the way to the target, there will be an additional deflection. If a bullet was pushed by the wind, or drifted with it, the accumulative effect would be so great that we'd have one helluva time hitting a 1000 target in a steady 25 mile an hour side wind.
External ballistics requires an open mind and, more importantly, an acceptance of Mother Nature's rules of physics. The rules sometimes seem to defy logic but once you realize that they cannot be bent or broken you are on your way to understanding. And, it helps to forget the comparisons with a swimmer in a river, an airplane flying in the wind, and a golf ball in flight. Examples like those only make it more confusing.0 -
I think this source makes it easy (or easier) to understand.
http://www.shootingtimes.com/2011/06/03/dont-blow-a-shot-in-the-wind
In short, a crosswind doesn't just blow a bullet sideways knocking it a fixed amount off target. Instead it deflects the bullet off its original flight path, changing the angle of the shot away from the shooter.
The problem with the original question, is that it overstates the effect of wind drift at short distances.
A 10mph crosswind will deflect a typical .308 bullet about 1 inch (or better yet, 1 MOA) at 100 yards, not 5 inches! If the wind stopped at 100 yards, then the bullet would hit a 500 yard target off from point of aim by about 5 inches.
Per the tables, a continuous 10mph wind would be expected to move the same .308 bullet about 22 inches at 500 yards. By extrapolation, a continuous 25mph crosswind would be expected to move the same bullet about 55" at 500 yards. To hit your target, you'd have to adjust your point of aim towards the wind by about 4.5 feet.
If that sounds like a lot, it is, but note that a 25mph wind is actually quite brisk. Its a "strong breeze" on the Beaufort scale, meaning you'll hear a whistling sound from overhead wires, and find it extremely difficult to hold/use an umbrella. EG:
http://www.youtube.com/watch?v=gI9JC4xxsic
Note also that bullets slow down normally during flight. As a result, the effect of wind is greater on bullets further away from the shooter, meaning that the RATE of change of direction of the bullet also increases the further it gets from the shooter.0
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