Wind Drift

K

K Hope

Member
Given a pure set of constants for Barrel twist, wind velocity and direction (symmetrically) does bullet drift the same (distance) for a right left wind and a left right wind?

Ken
 
A bullet does not drift because of a wind, it is deflected. A righthand twist will result in drift to the right and a lefthand twist will result in drift to the left. So, there is a difference in the net deflection although not usually noticable except and long distances. Long range Benchrest shooters are well aware of drift.

Ray
 
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Thanks Harold

I often question myself.
I guess its like the wife says: It's the operator not the machine.....

Ken
 
The answer to your question is yes, but some ranges will give you significantly more push from one direction than the other. Steve
 
Steve

Does this mean that: Range specific, a push hold could be proportionately different than a let off hold?

Thanks
Ken
 
K Hope said:
Given a pure set of constants for Barrel twist, wind velocity and direction (symmetrically) does bullet drift the same (distance) for a right left wind and a left right wind?

Ken
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No.

At 1000yds you will have an added effect of prox 1moa (significant) from something often termed "spin drift." The effect is to the right for a "right hand twist" (clockwise viewed from the breech) and visey varsey...

Another effect is that the LEFTWARD drifting bullet will also impact HIGH whilst the bullet which is drifting to the RIGHT of centerline will impact LOW. This is a drag effect and of the 5 "ballisticians" that I know of who've tried to explain it, 3 attribute it to the bullet yawing "nose high and into the wind" as it leaves the muzzle and the other two claim the exact opposite. :) (Three of the 5 have written articles in PS on the subject)

The simple fact is that a bullet will ALWAYS BE DRAGGED OVER BY IT'S BASE, in other words, a bullet follows it's TAIL, not it's nose.......


hth


al
 
Spin Drift

Al

I have heard talk of this from some. Is it possible to see this drift using a PPC at lets say 100 - 300yds?

Thanks
Ken
 
Al

The simple fact is that a bullet will ALWAYS BE DRAGGED OVER BY IT'S BASE, in other words, a bullet follows it's TAIL, not it's nose.......
Is this "drag over" velocity relative? Or in other words is it the CG weight that wants to pass as velocity slows?

Ken
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Click to expand...
 
Ken

I guess you didn't see my post or didn't get the drift of it.;)

At point-blank Benchrest it is there but so small as to be hidden by all other environmental factors. At long range (600 and 1000 yards) it is very evident and has to be taken into consideration.

I don't understand Steve's comment unless he is simply saying that some ranges get more wind from a particular direction.

All external ballistics are "velocity relative".

Get a copy of the Sierra manual. There is a great ballistics section in it.

Ray
 
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Is this "drag over" velocity relative? Or in other words is it the CG weight that wants to pass as velocity slows? Ken
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The bullet orients itself toward the center of pressure. So, if the wind is coming from the right, the bullet will point (slightly) to the right. That means it's base will "point" slightly to the left. The drag on the bullet, then, will be slightly right to left, so the bullet moves "left" as viewed from a downrange perspective. Movement from the wind has nothing to do with the Center of Gravity of the bullet, everything to do with drag.
 
K Hope said:
The simple fact is that a bullet will ALWAYS BE DRAGGED OVER BY IT'S BASE, in other words, a bullet follows it's TAIL, not it's nose.......
Is this "drag over" velocity relative? Or in other words is it the CG weight that wants to pass as velocity slows?

Ken
Click to expand...

Charles is right, BUT.... I get the sense of another question in your post.

You ask, "Is this "drag over" velocity relative?" and to this I must answer with, "I'm not sure what you're asking"....... The "drag over" is directly linked to the "RATE OF SLOWDOWN," the RATE of deceleration of the projectile. The faster a bullet is slowing down, the further it's dragged downwind. Initial velocity has negligible effect (within reasonable, usable shooting parameters) and CG has nothing to do with it, at least nothing directly.

hth

al
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Click to expand...
 
K Hope said:
Al

I have heard talk of this from some. Is it possible to see this drift using a PPC at lets say 100 - 300yds?

Thanks
Ken
Click to expand...

I was hasty...... :(

It's not possible to see the sideward component of "spindrift" but ......it IS not only POSSIBLE, but common to see it's exact 90 degree complement, "vertical drift"....

When a bullet is "blown left" it impacts high @100yds. When it's "blown right" it impacts low. While this isn't ever termed "spindrift" it is exactly the same set of forces just being applied from a different angle.

The "wind" applied to the bullet which produces "spindrift" is the upward "wind" from the bullet falling through the air at a rate of 32ft/sec/sec. Hence the effect gets much greater as the bullet falls longer, ie beyond 500yds.

sorry for the lack of clarity.

al
 
Spin Drift

Ray. Sorry I was not sure how to interpret your post # 3.

I have very limited understanding of ballistics however I am fascinated by the “Theory of Flight”.

Please note: Any further questions on my part are solely for my further understanding and are not of an opinionated nature.

Charles. You said: So, if the wind is coming from the right, the bullet will point (slightly) to the right. The bullet orients itself toward the center of pressure.

Please clarify: Would not any forces put on bullet from the wind (Top or Bottom) be equal? I would have thought that a bullet would orient itself around its mass or CG.


Al: I was referring to “Rate of Slow Down.” Velocity Relative.


Thanks ALL

Ken
 
Please clarify: Would not any forces put on bullet from the wind (Top or Bottom) be equal? I would have thought that a bullet would orient itself around its mass or CG.
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No.

You have to get over the notion of a bullet like a log floating in a river.

Ballistic theory, especially the basic tenants, is a topic ill suited for an internet thread. If you are a lay person, like most of us, try Harold Vaughn's book Rifle Accuracy Facts. If you have the math, Robert McCoy's will answer all your questions, and more.

For an internet site, try

http://bryanlitz.bravehost.com/GyroCor.html

for a start.
 
Charles

Yes, I must re-read Vaughn; not sure I will ever pick it up.
I am still trying to figure out your inference to bullet / log similarities. ;)

Ken
 
What I was talking about is that some ranges a left to right wind will push a bullet farther than the same velocity right to left wind. I don't know why but suspect that the layout of the terrain is the reason. But I have experienced this a number of times at various ranges, Fairfax Va. for one that comes to mind. Steve
 
The aforementioned Sierra Manual explains the whole thing a lot more clearly than most books that I have seen. It especially explains the difference between rotational (spin) drift and wind deflection. And it's very clear at explaining the results when there is a combination of both.

Plus, you also get a good loading manual as a bonus.;)

Ray
 
steve stanley said:
What I was talking about is that some ranges a left to right wind will push a bullet farther than the same velocity right to left wind. I don't know why but suspect that the layout of the terrain is the reason. But I have experienced this a number of times at various ranges, Fairfax Va. for one that comes to mind. Steve
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Steve

I'll bet it's the terrain. It (terrain) is probably adding a vertical component to the side wind which makes it appear to be more or less than it really is.

What do you think?

Ray
 
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