I have noticed that there is a lot of reference to wind drift on this forum, understandable. But what I see indicates that folks assume that a full value of wind, say from 3 o'clock or 9 o'clock results in a pure horizontal wind drift with no vertical component. With XTC and even long range with the conventional target (sling) it is small enough that most folks will not know it is there but it would seem like F Class folks with the more challenging target would be taking this into consideration. I could be wrong and have just missed this discussion.
Verticle Component of Wind Drift
- Thread starter chkunz
- Start date
Tim Singleton
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Toolbreaker
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;D ;D ;D Looks like it's a drift chart. Seems to also take spin drift into account. The numbers clocked on the outside indicate wind direction. Those numbers correspond to the numbers inside the chart, plotting impact points in relation to the wind direction, and also to the bullet's drift from a right-hand twist barrel.T-REX said:
It's called a wind rose and yes it does work.
IME I found Tony B.'s wind charts in his book to be more accurate. There are a few subtle differences. It also has the best explanation on how to interpret the info flags are telling you.
Pretty simple until the flags start disagreeing with each other, or you're at a range that defies the charts. ???
Pretty simple until the flags start disagreeing with each other, or you're at a range that defies the charts. ???
The horizontal component of wind produces a vertical deflection that lies on a line with a slope of about 1:10, with the left side higher than the right. That is, when wind is from the right, the bullet is blown to the left, and up about 1" for every 10" of lateral wind drift. And if the wind is from the left, the bullet is blown to the right, and down about 1" for every 10" of lateral drift. Of course, this is only for right-twist barrels. Direction of aiming, and northern/southern hemisphere have nothing to do with this effect. This is an aerodynamic effect (Bernoulli) of relative local wind speed at the bullet, and not related to the rotating earth-disc (both coriolis effects) or related to gyroscopic influences (the bullet is a spinning top lying on its side, "falling" forward, and never landing on a stable surface, but continually with its point in contact with a fluid (the air). Not only that, but the pressure on the pointy end, and conversely the pressure at the trailing (fatter) end is constantly changing due to drag, except that it's reversed for external versus internal ballistics, and omigoshIthinkmybrainwillexplode! Just ignore all of this and whip out the ballistic program on your cellphone.
If the OP is talking about vertical wind, such as coming up a canyon or shooting through a microburst (?), that is just another wind vector. However, there's no program that takes this into account. You would have to draw a topographic model of the particular shot in question, and run it through all the applicable calculations, for each parcel of wind through which the bullet will pass. (Pictorial wind models to do this are available. Nascar played with them at one time, and still may, for safety's sake.) By the time you've done that, the target will have moved, and you can start over. For this, it's easiest to fire a bullet, and correct based on the impact. For F-class, the terrain is sufficiently flat (or at least will not change from one shot to the next) such that this is irrelevant. Anyway, there's no way to check vertical wind, unless you're shooting at a major airport with microburst detection capability, or you can build your own scintillometer and program it in two dimensions. Buena suerte!
If the OP is talking about vertical wind, such as coming up a canyon or shooting through a microburst (?), that is just another wind vector. However, there's no program that takes this into account. You would have to draw a topographic model of the particular shot in question, and run it through all the applicable calculations, for each parcel of wind through which the bullet will pass. (Pictorial wind models to do this are available. Nascar played with them at one time, and still may, for safety's sake.) By the time you've done that, the target will have moved, and you can start over. For this, it's easiest to fire a bullet, and correct based on the impact. For F-class, the terrain is sufficiently flat (or at least will not change from one shot to the next) such that this is irrelevant. Anyway, there's no way to check vertical wind, unless you're shooting at a major airport with microburst detection capability, or you can build your own scintillometer and program it in two dimensions. Buena suerte!
"about 1" for every 10" of lateral wind drift" This seems to be about what I am remembering. I am remembering about eighth to one for smallbore prone shooters. May not be enough to consider for most folks but might be worth considering for the better shooters if they are having to make significant changes due to a significant wind change.
butchlambert
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Speedy's wind chart? I don't think so.
That is why I brought this up. I have not seen this mentioned in a long time and it seems like with the level of performance we are seeing with the long range shooters these days someone would be noticing. I am wondering if what some folks are referring to as getting vertical in their groups could be partly this effect coming into play.jr600yd said:
Bryan Litz Ballistics
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There are three different vertical considerations to make with wind.
One is simply the effect of the wind following the terrain and developing an 'updraft'.(or downdraft) In this case, the wind is deflecting the bullet same as a cross wind, just up or down. You usually don't see much of this if you're shooting over flat ground, more so when shooting over canyons, hill to hill, etc.
The other effect is what's been discussed (the 10 O'clock to 4 O'clock slant of a group). This happens due to a mechanism called aerodynamic jump. When the bullet emerges from the muzzle into a crosswind, it weathervanes into the net airstream, which will be at a slight angle due to the cross-wind. The bullet sees a 3000 fps headwind, and a 15 fps (10 mph) crosswind, so the bullet has to weather-vane less than 1/2 of one degree. As the bullets axis is torqued to realign that slight angle, it reacts with a series of precession cycles, the result of which cause a slight vertical deflection called 'aerodynamic jump' (AJ).
AJ is a fixed angular amount at the muzzle, meaning that if it's 1/2" at 100 yards, it will be 5" at 1000 yards. It's not a parabolic growth like wind drift which might be 1" at 100 but 80" at 1000. This is because horizontal wind deflection acts on the bullet for it's whole flight, while AJ is a lunch effect that's established within 15-20 yards from the muzzle. That's why it's called 'jump'.
One place AJ used to cause problems was for .50 cal waist gunners on WW2 era bombers. They're firing into 100's of mph of crosswind, and depending on which side they were firing from would determine if the jump was up or down. Not a precision shooting application, but high crosswind.
The magnitude of AJ depends on bullet stability, with higher stability producing greater AJ. For a 10 mph crosswind and typical LR rifle, you'll see something like 0.2 MOA of AJ compared to no wind.
In a long range shooting match such as BR or F-class, it's not likely that you'll have to correct for AJ. Assuming you shoot sighters in the prevailing wind, AJ is the same for every shot so if the wind is 15 mph +/-5 mph crosswind (a difficult condition), the worst you'll see on the target is less than a 1/4 MOA click of vertical from AJ. But you could see much bigger vertical effects from actual vertical wind currents, or direction changes (head/tail component).
Usually, if you shoot big vertical in big wind it's due to the vertical wind currents that develop over terrain and the general turbulance of the air, not AJ.
The final way high winds can affect vertical is the head-wind acting to slow the bullet more, and a tail wind acting the other way. These effects are minor compared to crosswind, but if you have a big direction change mid string, it may show up as a few inches of vertical at 1000.
-Bryan
One is simply the effect of the wind following the terrain and developing an 'updraft'.(or downdraft) In this case, the wind is deflecting the bullet same as a cross wind, just up or down. You usually don't see much of this if you're shooting over flat ground, more so when shooting over canyons, hill to hill, etc.
The other effect is what's been discussed (the 10 O'clock to 4 O'clock slant of a group). This happens due to a mechanism called aerodynamic jump. When the bullet emerges from the muzzle into a crosswind, it weathervanes into the net airstream, which will be at a slight angle due to the cross-wind. The bullet sees a 3000 fps headwind, and a 15 fps (10 mph) crosswind, so the bullet has to weather-vane less than 1/2 of one degree. As the bullets axis is torqued to realign that slight angle, it reacts with a series of precession cycles, the result of which cause a slight vertical deflection called 'aerodynamic jump' (AJ).
AJ is a fixed angular amount at the muzzle, meaning that if it's 1/2" at 100 yards, it will be 5" at 1000 yards. It's not a parabolic growth like wind drift which might be 1" at 100 but 80" at 1000. This is because horizontal wind deflection acts on the bullet for it's whole flight, while AJ is a lunch effect that's established within 15-20 yards from the muzzle. That's why it's called 'jump'.
One place AJ used to cause problems was for .50 cal waist gunners on WW2 era bombers. They're firing into 100's of mph of crosswind, and depending on which side they were firing from would determine if the jump was up or down. Not a precision shooting application, but high crosswind.
The magnitude of AJ depends on bullet stability, with higher stability producing greater AJ. For a 10 mph crosswind and typical LR rifle, you'll see something like 0.2 MOA of AJ compared to no wind.
In a long range shooting match such as BR or F-class, it's not likely that you'll have to correct for AJ. Assuming you shoot sighters in the prevailing wind, AJ is the same for every shot so if the wind is 15 mph +/-5 mph crosswind (a difficult condition), the worst you'll see on the target is less than a 1/4 MOA click of vertical from AJ. But you could see much bigger vertical effects from actual vertical wind currents, or direction changes (head/tail component).
Usually, if you shoot big vertical in big wind it's due to the vertical wind currents that develop over terrain and the general turbulance of the air, not AJ.
The final way high winds can affect vertical is the head-wind acting to slow the bullet more, and a tail wind acting the other way. These effects are minor compared to crosswind, but if you have a big direction change mid string, it may show up as a few inches of vertical at 1000.
-Bryan
Bryan,
Are you saying AJ does not happen down range? When a bullet enters a cross wind from none does the bullet not precess into the new vector causing jump?
Are you saying AJ does not happen down range? When a bullet enters a cross wind from none does the bullet not precess into the new vector causing jump?
Bryan Litz Ballistics
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My explanation was assuming constant wind along the flight path.
If the bullet encounters a change downrange, the same mechanism would happen but rather than a jump its more of a gradual climb for a relistic increasing wind. But it can never climb to a greater level than if it encountered the same wind right at the muzzle.
If the bullet encounters a change downrange, the same mechanism would happen but rather than a jump its more of a gradual climb for a relistic increasing wind. But it can never climb to a greater level than if it encountered the same wind right at the muzzle.
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