Is Wind drift linear?

Kraig's right about spin drift. It's not much as he says. For example, a .30-06 with a 172-gr. FMJBT bullet leaving at 2700 fps has about 7 inches at 1000 yards. If you have everything perfect and this is what you get, then set your sights between 1/4 and 1/2 MOA left for a zero and the error for drift will be no more than 3.5 inches at 1000, half that at 600, 1/4th at 300 and so on.

If you can judge cross wind values from zero to 1000 yards across your bullets trajectory path accurate enough to make exact wind corrections with no more than a 1/8 MOA error, then you need to be concerned with spin drift. To date, I don't know of anybody that can do that.

One other thing; you and your shooting stuff has to do no worse at 1000 yards than 3 inches maximum spread all the time or you will never see the effects of spin drift.
 
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Subsonic bullets are also subject to vertical drift, due to rotational friction against the wind. For instance, say a 10 mph wind at 9:00 will move a .22 LR about an inch right of center. The drop will be approximately 1/5 the horizontal. Conversely, wind from 3:00 will cause the bullet to rise about 1/5 the horizontal.

Wind from other various clock positions will create lesser combinations of drop or rise as well as deflection, but any wind angle from 12:00 to 6:00 will cause the bullet to rise somewhat and from 6:00 to 11:45 or so will cause a drop component. Winds close to 12:00 can cause either rise or drop, unpredictably, so rimfire benchresters try to hold the shot and wait for the wind to change.

Swirling winds on bermed ranges can be hell to rimfire bench folks; been there!
 
I think I'm beginning to understand why the only place I have ever managed one-hole groups @ 50 yards with a .22 is in an indoor range.

I don't see why the vertical deflection from bullet spin in a crosswind is limited to subsonic bullets though.

Maybe that's why those fast twist muzzleloading barrels can't compete with the slow twist barrels in matches, even though they can shoot very accurately in ideal conditions.
 
What have you guys found to be the most reliable way when reading wind (mirage, leaves...) if there are no flags? Do you use any handheld devices or other portables?
 
I don't see why the vertical deflection from bullet spin in a crosswind is limited to subsonic bullets though.
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Its not, the difference is TOF, or time of flight. The longer the bullet is exposed to the wind, the more the wind affects it.

What have you guys found to be the most reliable way when reading wind (mirage, leaves...)
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All of the above, but I like mirage the best. What we need to understand, is wind is different at different altitudes. Meaning, if your shooting prone, what the wind is doing at 2-3 feet above the ground is not what the wind is doing at the top of the arc of the bullet path.

To see this, use two range flags. One at the bottom of the flag pole, and one 20 feet in the air. You will see, most of the time the flags are indication different wind velocities. May not even be blowing the same direction.

Now mirage is different, you can focus your scope to read the mirage at any place you want to, ground level, 20 ft in the air, across a canyon or where ever (just make sure the scope is NOT focused past the target, that will give you a false reading).

Mirage is not hard to learn, just take practice. Take your wind meter and spotting scope out to the field (don't have to be a range, could be your back yard, a parking lot or what ever).

Look in the scope and observe what the wind is doing. Now take a wind reading. With practice you can get pretty good and accurate.

Same thing with leaves, grass, and trees. Take your wind meter with you on your walks. See what the wind is doing to the leaves, grass, trees, whatever, and check your wind meter to see how much wind it takes to make the leaves, grass & trees do what they do.
 
I use a Dwyer wind gauge to read the wind speed at the firing line. Cheap and accurate. Then use a constant for the bullet and its muzzle velocity to calculate corrections based on wind speed and directions.

Here's a table showing the wind speeds above the line of sight:

8029408404_bdcc406050_z.jpg


If you look at the trajectory path of a bullet, it spends only about 25% of its time at the top of its arc where wind speed's the fastest. 50% of its time in the middle wind speed range and about 25% in the lowest speed range.

The following's a table showing how much the wind has at different ranges for a given crosswind across the entire trajectory:

8005236761_fa9ce73231_z.jpg
 
The range we frequent (finally) put flags at 100 yard intervals all the way downrange.

This has served to frustrate and confuse even more, because now we KNOW what we used to only suspect- that the wind is doing something completely different at every flag (and no doubt, in between as well).

I have no doubt that shooting on an open plain or a range that's not surrounded on all sides by twenty-foot tall berms would be much simpler. Even a 5 mph wind swirling inside a punchbowl is going to be challenging.

Bottom line, it's all fun to talk about theory, but just get out and send 100 rounds as often as you can- and try to learn from the frustration.

This is where a good brake- if you don't have a spotter- is indispensable.
It's more important to spot your misses, than your hits....or it's just a waste of expensive ammo. Pay attention to the conditions when you break the trigger- make your adjustments and keep good notes.
 
Using a spotting scope to read (see) the mirage (heat waves); lesson 1:

Get a 20X to 25X spotting scope, mount it on a tripod so it's very steady. (NOTE; you can also use a rifle scope of at least 15X that has an adjustable objective so you can focus it at some distant range.)

Go outside on a warm day when the wind's blowing a little bit (no hurricanes at all) to someplace where you can see at least half a mile over reasonably flat ground.

Point the scope at something about half a mile away, then focus it so the image is as sharp as you can get it as you see it.

Note the direction the wind is blowing; left to right or the reverse thereof.

Look through your spotting scope at the thing you focused on then change focus to something closer; move the focus adjustment very slowly.

As you change focus to something closer you should see the wrinkling heat waves (mirage) become clearer and easier to see as they look like running water moving across the scope's field of view. It's the wrinkle close to and just above what your looking at that counts the most.

Move focus as close to where your are as possible so you can see how the mirage appearances changes with focus.

Sit down, take a break then do this over again.

What happens is as the light rays from the far away things go through the air to your eyes, their direction gets changed by the air temperature in it and how its moved around by the cross wind. Find a focus point where you can see the mirage clearly then watch it speed up as the wind speed increases or slow down as the wind drops.

Watching the mirage (reading the wind in competitive shooting language) will let you know whether to move your sights into the wind if it speeds up or away from it if it slows down. Doing this keeps your shots falling at the same place.

How much to move your sights for a given visible wind change? That's lesson two.
 
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I disagree on the "reaiming" by a short burst of air close to the muzzle being worse than the same burst close to the target. As long as your bullet is well stabilized, it stays on it's original track, and only gets pushed sideways for a given time. The only difference would be due to the differential speed at muzzle and at target, and that effect is contrary to the one described, close to the target the bullet is slower and would be affected more by as side wind.
 
What is "reaiming?" Never heard of that term.

Do you think a bullet that's been pushed sideways by a cross wind blowing to the left, then that wind stops, that bullet will make a right turn back to parallel to its path before the wind moved it and strike the down range target a distance equal to its position left of the line of sight when the wind stopped?
 
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I disagree on the "reaiming" by a short burst of air close to the muzzle being worse than the same burst close to the target. As long as your bullet is well stabilized, it stays on it's original track, and only gets pushed sideways for a given time. The only difference would be due to the differential speed at muzzle and at target, and that effect is contrary to the one described, close to the target the bullet is slower and would be affected more by as side wind.
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Now I'm really confused. Wish I hadn't read that.
 
Picher's #22 post...is probably correct for a firearm with a right hand twist --- for a left hand twist, the vertical direction would be opposite.
I'm not a expert on the subject of wind deflection, so if I make any mistakes --- please correct me.
Wind deflection is based on a arc. A bullet...that is affected by the wind as it first leaves the muzzle, will have a greater horizontal arc deflection on the bullet, than a bullet that is affected by a wind downrange. At very long distances...wind will have a much greater horizontal arc deflection effect on bullets downrange; as the bullet slows down.

Besides wind flags, mirages, wind meters, wavy trees and flying leaves --- I'am trying {for 22 rimfire} to dope the wind speed and direction...by the way the wind hits my face or neck --- in a way that I can determine wind speed and direction, so I can instantly correct holdover's --- a steady wind helps.

David Tubb... has an excellent book on wind deflection --- along with other shooting accuracy tips.

Tubb...focuses his spotting scope, ten yards short of the target --- so he can read wind mirages.
 
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Erno86 mentions:
David Tubb... has an excellent book on wind deflection --- along with other shooting accuracy tips.

Tubb...focuses his spotting scope, ten yards short of the target --- so he can read wind mirages.
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I doubt that. I don't know of anyone who can resolve focus good enough to discriminate between a perfect focus on two things 10 yards apart at 1000 yards. Even with a spotting scope with a 100 mm diameter spotting scope objective lens. I've tried it with the finest optics on this planet and with near 20-10 vision most of my life, could not resolve focus between two things 10 yards apart at 1000 yards.

I'm surprised if David really put that in print. Well, kind of surprised. Having known David since he was a teenager back in the 1970's and shot many a match with him and his dad, George, David's well known in High Power Rifle competition as one who "stretches" things to gain an advantage. I've watched him adjust focus on his spotting scope every time he gets ready to shoot. If he really did focus at the same place all the time, he would not have to change focus on his spotting scope.

Most match rifle competitors focus their scope somewhere between them and the targets range so they can see it wrinkling across their field of view centered just above the target image. You need to see that mirage wherever its at. Shooting 5 days in a row on the same shooting range at targets from 200 to 1000 yards away, I've noticed I have to change focus for each target distance depending on which direction the winds come from as they ain't uniform across the low hills and valleys around the range. Whatever focus gets you the best mirage is what you use. It can also change from time to time during the day.
 
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My post was in response in to BLE's #11. And yes, the bullet will continue parallel to it's original path. Otherwise you wouldn't get the linear deflection for constant wind. If the bullet would change direction, the deflection would be exponentially increasing with distance (which everyone agrees it is not).
 
My post was in response in to BLE's #11. And yes, the bullet will continue parallel to it's original path. Otherwise you wouldn't get the linear deflection for constant wind. If the bullet would change direction, the deflection would be exponentially increasing with distance (which everyone agrees it is not).
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Actually, wind drift is exponential with distance in a constant wind.

Here's the calculation of a standard velocity .22 long rifle bullet in a 10 mph cross wind.

25 yards 0.3 inches
50 yards 1.3 inches
100 yards 5.1 inches
200 yards 19 inches

It's linear to wind strength, exponential to distance.
 
B.L.E.'s astute observation:
Actually, wind drift is exponential with distance in a constant wind.
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Correct.

Another way to grasp this reality is that bullet moves sideways with the wind at the same rate from muzzle to target in a constant crosswind. For each tenth of a second it goes down range it will travel a shorter distance. So, for each tenth of a second it goes down range the more its trajectory curves to the side.
 
Furthermore, if the bullet hits a gust of wind at 25 yards and there is dead calm the rest of the way to the target, the bullet will continue on its new path and get further and further away from the original path, just as if it had been deflected by a twig or blade of grass.

If it hits a left gust at 25 yards, and then a right gust at 50 yards, now it will fly roughly parallel to its original path but displaced sideways a little.
 
Linearized not linear

So I'll throw in the Physics spoiler, and a way to maximize the hit potential in the future: Virtually none of the variables or factors that are generally considered in ballistics calculations are linear when it comes to turbulent or laminar flow. The charts that are used are subset of multi-ordered (like 5th to 9th order) differential equations (the bane of even hard core engineers). A Psychometric chart (like to one at Wikipedia here http://en.wikipedia.org/wiki/File:PsychrometricChart.SeaLevel.SI.svg ) is pretty simple in relationship to predicting the precise location of a projectile at 500 meters.

I only mention this as if you start to interpolate some of the numbers outside their current range (ie "if it works at 300 yards then 600 yards must be twice / half the value").

If you want to take the easy route out, look for laser guided projectiles in the near future. DARPA has developed a pretty sophisticated device. Expect to see significantly lower cost guided bullets that are more like laser guided bombs often called 'bang bang' guidance systems, that require the laser illumination to be within a few degrees of the flight path. Either can can hit the left or the right nostril of a deer at 1000 yards 90% of the time.

Ain't math wonderful?
 
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