I've asked this question on other boards and it seems there is always at least one that prefaces their answer with "It's simple physics" or some such derogatory comment. but being the eternal optimist I'll ask it here and see if I can get a straight answer:

Is the effect of wind on a bullet cause it to A.Drift or B.Change direction?

an example is: The firing line is 600 yards from the target. There is a 20 mile per hour wind blowing from 9 9'clock to 3 O'clock but this wind is only blowing from the muzzle to the 100 yard marker. The wind is calm from 100 yards to 500 yards. From 500 to 600 yards there is a 20 mile per hour wind blowing from 3 O'clock to 9 O'clock. For purposes of the example consider the velocity of the bullet and it's BC to remain constant.

If the wind only drifts the bullet, the winds will offset and there will be no effect- it would drift to the right for the first hundred yards, then fly parallel to the line of sight from 100 to 500 yards, then it would drift to the left during it's flight from 500 to 600 yards, ending up where it would have been without the wind (not counting the increased time of flight & subsequent drop).

However, if the wind causes the bullet to change direction the wind at muzzle to 100 yards would cause the bullet to diverge from the line of sight not only from 0 to 100 yards, but it would continue away from the line of sight to 500 yards, at which point the wind would blow the bullet back toward the target, but only to the extent that it offset the amount of deflection occurring between the muzzle and 100 yards. It would be off target by the amount of course change that occurred from 100 to 500 yards.

So which is it? Thank you.

quote:

an example is: The firing line is 600 yards from the target. There is a 20 mile per hour wind blowing from 9 9'clock to 3 O'clock but this wind is only blowing from the muzzle to the 100 yard marker. The wind is calm from 100 yards to 500 yards. From 500 to 600 yards there is a 20 mile per hour wind blowing from 3 O'clock to 9 O'clock. For purposes of the example consider the velocity of the bullet and it's BC to remain constant.

There is an obvious problem with your example. The effect of wind on a bullet is dependent on the amount of time the bullet is subjected to the wind not on how far the bullet moves. The time of flight from 0-100 yards will be significantly shorter than the time of flight from 500-600 yards.

Long range shooters estimate the average or effective wind and apply that to the total time of flight to the target. If there is much wind at all, especially over varied terrain, it will not be precise. That is one reason true first round hits at very great distances are so difficult. It also is why shooters use spotters. Calculations get them close but only after they can see where the rounds are really going can adjustments be made to put the rounds on target.

quote:

For purposes of the example consider the velocity of the bullet and it's BC to remain constant.

OBVIOUSLY



the question is: does wind drift or deflect bullets?

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the question is: does wind drift or deflect bullets?

Both. Drift is obvious, deflection not so obvious. Because a bullet is rapidly spinning on its axis there is a gyroscopic effect working to force the bullet to follow a crosswind. The bullet will be defected toward the direction the wind is blowing.

Ray,

Rather than trying to answer a complicated question here, I suggest you get a copy of APPLIED BALLISTICS FOR LONG-RANGE SHOOTHING by Bryan Litz - Chapter 5 deals with this problem.

If you already don't have this book, buy it - it's worth every penny.

Also, you can actually calculate complex wind solution like you describe with the app called BALLISTIC AE

See...

https://www.youtube.com/watch?v=hHxhIZHUUsA

By playing with the APP, you'll be able to answer you own questions regarding complex wind solutions, which can be much more complicated than your question.

AIU

Ray,

I have the app and I went ahead and solved the problem you pose...

(The firing line is 600 yards from the target. There is a 20 mile per hour wind blowing from 9 9'clock to 3 O'clock but this wind is only blowing from the muzzle to the 100 yard marker. The wind is calm from 100 yards to 500 yards. From 500 to 600 yards there is a 20 mile per hour wind blowing from 3 O'clock to 9 O'clock. For purposes of the example consider the velocity of the bullet and it's BC to remain constant.)(Bullet velocities do not remain contant, and in this case, if they did the effect of the equal opposite wind from 5-600 yds would be even less.)

308 168 Berger Hybrid at 2700 fps at sea level

Needed wind correction for a 500 yd target 2.46 MOA

Needed wind correction for a 600 yd targe 2.16 MOA.

Conclusion: that last 100 yd opposite 20 mph wind did not put the bullet back on target, and the first 100 yd 20 mph wind continued to have a significant effect, although some correction occurred in the last 100 yds.

Most say the wind near the muzzle is more important, because its effects or deflection continues for the duration of the bullet's flight.

The findings in this solution would confirm that impression.

Actually, the original situation was overly complicated. A better example would be:
9 to 3 wind for muzzle to 100 yards, then calm. Say the bullet is 3 inches right of line of sight at the 100 yard line. If the wind only causes drift, then the remainder of bullet travel would be parallel to line of sight, but if the wind caused change in direction, the bullet would continue to divert from the line of sight.
from above posts, it appears that the bullet would continue to move away from the line of sight, but to a lesser degree than when it was being blown by the wind.

I seems to me intuitively obvious that the wind near the muzzle changes the direction of the bullet, so that it continues to move in a slight sideways direction even if the wind further downrange is not present. For deflection to occur, the bullet must take a different direction, and in the absence of a continuing force further downrange, will continue in the new direction. All who shot competitively have experienced a wind near the line causing a deflection far greater than a wind near the target. When spotting for BPCR silhouette, most good spotters largely ignore the wind for the last 1/3 of the distance to the target and concentrate on the wind closer to the line, where it has more effect, as AI's example illustrated.

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Originally posted by ClaMar:
I seems to me intuitively obvious that the wind near the muzzle changes the direction of the bullet, so that it continues to move in a slight sideways direction even if the wind further downrange is not present. For deflection to occur, the bullet must take a different direction, and in the absence of a continuing force further downrange, will continue in the new direction. All who shot competitively have experienced a wind near the line causing a deflection far greater than a wind near the target. When spotting for BPCR silhouette, most good spotters largely ignore the wind for the last 1/3 of the distance to the target and concentrate on the wind closer to the line, where it has more effect, as AI's example illustrated.

Yes, this is what happens - wind near the muzzle is more important than wind near the target.

Wind near the muzzle causes a change in angle of flight which continues to move the bullet away from target center.

This is exactly what the complex wind app shows.

Good!! the answer to the original question then is B.

thanks for the clarification.

I do not believe the answer to the question is (b). The bullet drifts. If you have a wind between the muzzle and 100 yards only, it will impart a lateral velocity to the bullet which will remain relatively constant through the flight of the bullet. If the wind is constant all the way out to, say, 1000 yd, the rate of deflection will increase. If the wind only occurs in the last 100 yd, the lateral velocity imparted by the wind will be slightly greater simply because the bullet is slower so that the wind acts upon it for a greater length of time. However, since it will then hit the target (we hope), drift will be minimal. Regards, Bill

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Originally posted by Ackley Improved
I suggest you get a copy of APPLIED BALLISTICS FOR LONG-RANGE SHOOTHING by Bryan Litz

+1

Long range bullets trace. i.e. they point into the apparent wind like an arrow, which is why we see spin drift and elevation due to wind. So in your example with wind for part of the trajectory, the trajectory is bent by the windy section and will continue on its new path afterwards at an altered angle. It will not head back the other direction, or even back parallel to the original point of aim without wind coming from the other direction.

The situation can be a little different for a short stubby bullet fired with high twist. These can be over-stabilized and will not necessarily point into the wind, they will tend to barrel through at an angle. They will also drift in wind, but spin drift will be less pronounced. So again in your example, the bullet will be pointed in a different direction by the windy section of the trajectory, but you won't see as much of a change in elevation due to wind.

This is also why wind at the shooter's position is more important than wind at the target. A gust of wind at the start of the trajectory will change the rest of it.

I totally agree with AI user.Get the book;there are so many variables that this can not be answered on a chat forum.Good reading as well + as always,accuracy is our end goal + result.

What about the earth's spinning, at 600maybe an inch ?? Time of flight might be more if it's not real fast...about 4 inches at 1000 with my Dasher ...

Been shooting Long Range matches for several years now and was taught sometime ago that wind correction should be taken for what wind you estimate for the first 1/3rd. of the range you are shooting. 1000yds. would back focus my spotting scope to approx. 300yds. and adjust accordingly. The bullet flight is impacted the most by the wind it experiences when first leaving the muzzle. Is it precise in all cases, no it is not, but there is nothing you can do to correct for wind at the target be it man or beast. Trick is to determine as closely as possible the clock direction the wind is coming from for as in the above example, 3 and 9 o'clock are "full value" winds requiring more adjustment than a wind from say 2 to 8 o'clock, less adjustment. Then you have to watch closely for "switching wind" which makes it real sporty. Reading the wind and making good decisions on adjustment comes from many, many rounds down range in various wind conditions and there are numerous books on the subject, but there is no substitute for "time behind the gun..."