WIND: bullet drift or direction change?

[Ray B]

I'm wondering if wind "drifts" the bullet or changes it's direction. Example: a bullet is fired at a target 500 yards away. From the muzzle and for the first 100 yards there is a 20 mph crosswind. Lets say that the wind caused the bullet to deviate from the line of sight 1 foot in that 100 yards. From 100 yards to the target there was no further wind. If the wind merely drifted the bullet the bullet would impact 1 foot to the side of the point of aim. However, if the wind changed the direction of the bullet, the bullet would impact possibly 5 feet to the side. Any ideas on which it is or is it a combination of the two?

 

[nztimb]

Once wind has an effect on a bullet, depending on the force of the wind, the deviation from original point of aim will continue untill impact point so drift is a continuous force but if there is a sudden change to still air then the bullet flight has changed to the drift direction at moment of still air contact and should act as if the sights had been alligned toward the new contact point. In short continuous wind causes wind continuous drift but wind then still air causes direction change. Continuous wind is easier to allow for.
Wind is a force on the side of the bullet just as the powder charge burn has a force on the base of the bullet and the ceasation of one or both of those forces ceases to effect the flight of the bullet

 

[Inline6]

Not all bullets are going to act the same. If shooting a 22 the wind inside of 100 will have a greater impact than a 556.

Bullet shape and speed have a lot of bearing as to what happens in the wind. The other part to the equation is how high up does the bullet go before it drops back down? The higher you go the faster the wind, compared to surface winds.

There is no real shot answer. We would also have to get into aero dynamic jump. The list goes on and on.

@Von Gruff did a good job of providing an answer. Just realized the wind does more than pust a bullet left or right.

 

[Ray B]

Here is the question:
Both bullets are fired into wind that is blowing perpendicular to direction of fire. but it is only blowing for a short distance. The remainder of the distance to the target the air is calm. there are two answers. The bullet on the left is "drifted" by the wind but maintains it's course- when the wind stops it continues effectively parallel to the line of sight.
the bullet on the right is affected by the wind by changing it's direction. Initially the bullet path is similar to the bullet on the left, but since it's direction wa changed by the wind, when the wind stops, the bullet continues on a path that is at an angle to the line of sight.
Options are left, right, neither.

 

[Tra3]

I’m curious about this answer. I’m inclined to think it is the right option.

 

[Inline6]

Here is the question:
Both bullets are fired into wind that is blowing perpendicular to direction of fire. but it is only blowing for a short distance. The remainder of the distance to the target the air is calm. there are two answers. The bullet on the left is "drifted" by the wind but maintains it's course- when the wind stops it continues effectively parallel to the line of sight.
the bullet on the right is affected by the wind by changing it's direction. Initially the bullet path is similar to the bullet on the left, but since it's direction wa changed by the wind, when the wind stops, the bullet continues on a path that is at an angle to the line of sight.
Options are left, right, neither.

The answer is C which is in-between your two scenarios.

Bullets do not stop moving like A.

B is what a full value consistent wind would look like.

 

[sgt_zim]

The bullet will continue to drift in the direction the 1st 100 yards of perpendicular wind pushed it. If there is nothing to counteract the force of the wind after that 1st 100 yards, it will still continue to drift. It will certainly drift less than if the wind were continuous along the bullet's 500 yard flight path, but it will continue to drift nonetheless.

Newton's 1st and 2nd laws don't stop having an effect just because the wind ceases. A force was applied to the bullet, and the effects of it will be realized along the entire flight path.

The question isn't if it will continue to be affected, it is only "how much will it be affected?". The answer is "somewhere between what a continuous wind would have done, and what it would look like if there were no wind acting on it at all." If the initial drift at 100 yards is 6", at 500 yards, the drift will be somewhere between 6" and what a continuous wind out to 500 yards would have done.

For the purpose of warfare, the difference is likely so small as to make no difference. For hunting, the difference could be enough that a shot would be unwarranted.

 

[Ray B]

If the wind drifts the bullet and this drift has an element of lateral momentum then the possibilities have four aspects. the drawing shows: Left bullet, same as the previous drawing, bullet drift in response to wind, then no drift when air is calm. middle left bullet is same drift as first bullet. but when air is calm the bullet has a small amount of continued drift due to the original push of the wind. Middle right bullet has steady wind from muzzle to target. Each segment of travel has the same drift as the first bullet- that is, five segments of drift due to the constant wind and no increase in lateral movement. Far right bullet has wind during the entire range of travel but each segment shows the drift caused by the wind over that portion of distance plus the added change in direction caused by the accumulated wind force. Bullet four shows a bullet travel that would use a formula resembling an objects response to gravity in that the deflection due to wind would be an acceleration.

 

[Inline6]

We are talking about a lot of hypothetical, the only thing I have seen that would be close to this. If you were in a field and the edge of a forest was infront of you. If I had to take the shot I would use 75% of a full value wind call. That would be my guess with one of my fast 6mm (14" @ 10 mph FV) if you took a 22lr (117" @ 10 mph FV) that distance the result would be different. I would probably call 90% of full value.

The rub comes in when we start talking about target size, that is your margin of error. Then direction of wind and direction of rifling. The strong the wind the more the bullet will ride up or down. Again how big is the target?

To be able to prove the theory is going to be difficult. I'm sure someone like Bryan Litz or Jayden Quinlan could give the better answer.

 

[375 Ruger Fan]

Very interesting question and comments. I did a little research and think the right bullet is more likely than the left. The vector of the bullet changes.

Actually, a couple of interesting articles attached.

Wind Doesn't Blow Bullets — Ron Spomer Outdoors

The persistent myth that wind blows bullets off target is a misconception. Light, small caliber bullets are not blown more than larger caliber, heavy bullets. Wind is actually redirecting the bullet's path, and a simple experiment proves it. Here's what's really going on with wind drift.

www.ronspomeroutdoors.com

 

[fourfive8]

Temporary side wind effects on bullet path? Hmm?

The questions to ponder could include: Does the wind temporarily push the bullet sideways or does it change the bullet’s direction of flight? If it changes bullet’s direction of flight does that imply changing rational axis orientation of bullet? If that is so then the physics of gyroscopic angular momentum may need re-evaluation. Just thinking out loud

Interesting to watch bullets in flight from rear angle as they experience variable wind direction or velocity between gun and target.

 

[Ray B]

I am talking NO hypothetical and amount of acceptable error is not an issue. What I have gleaned from the above responses is that moving air (wind) grips the bullet and carries it, much like a person swimming across a river. this movement I call drift. Additionally the movement of the bullet has resultant inertia which accumulates in the form of change of direction. The swimmer is no longer swimming directly across the river, he is swimming at a slight diagonal to the original direction. The bullets response to wind would be the total of the drift and the direction change. While the drift would be a constant, the direction change would be a function of bullet travel after the change. Another drawing. Left bullet encounters wind at muzzle and for the first 100 yards. Middle bullet encounters the same amount of wind, but the air is calm from the muzzle until the last 100 yards to the target, where the wind is same amount as left bullet. If this is correct, the bullet that encounters the wind at the muzzle will be moved farther from the line of sight. The right bullet has wind blowing left to right at muzzle for 100 yards, then calm, then when 100 yards from target encounters right to left wind of equal strength as the wind at the muzzle. With the right bullet if the bullet were strictly drifted, the wind would offset and the bullet would land in line of sight, but since the bullet had lateral movement generated by the wind the bullet would land slightly to the right of line of sight. Because of this lateral movement of the bullet resulting in change of direction, wind at the start of the bullets flight has more effect than wind near the target.

 

[bowjijohn]

Temporary side wind effects on bullet path? Hmm?

The questions to ponder could include: Does the wind temporarily push the bullet sideways or does it change the bullet’s direction of flight? If it changes bullet’s direction of flight does that imply changing rational axis orientation of bullet? If that is so then the physics of gyroscopic angular momentum may need re-evaluation. Just thinking out loud

Interesting to watch bullets in flight from rear angle as they experience variable wind direction or velocity between gun and target.

Brian Litz deals with this topic in great detail in chapter 5 of his book '' Applied Ballistics for the long distance Shooter''

Wind deflection is a function of

1. Cross wind speed
2. Lag time

Lag time is a function of

1. Time of flight (which itself is effected by ballistic coefficient and muzzle vel amongst other factors)
2. Theoretical time of flight in a vacuum

It has to do with a bullet's tendency to nose into wind, introducing a sideways (lateral) force in additional to the slowing force (drag?) in the opposite direction to that of the direction of travel (which is in line with the axis of rotation of the bullet) - (resolution of forces)

I can't explain it well as I barely have a grasp of it myself - what it ISN'T apparently is wind blowing the round off course

j

PS - I'm sure someone will be along who has a better grasp of ballistics than I, and explain this topic better

 

[375 Ruger Fan]

Because of this lateral movement of the bullet resulting in change of direction, wind at the start of the bullets flight has more effect than wind near the target.

Correct

 

[Forrest Halley]

Wind on a .22 is a groundhog's saving grace.

 

[mark-hunter]

Here is the question:
Both bullets are fired into wind that is blowing perpendicular to direction of fire. but it is only blowing for a short distance.

There is no force to alter axis of bullet as per scheme A. (to change heading)
Bullet stays directed in the heading of aim, moreover it is stabilsid by gyroscopic effect of the spin.

What happens with gyroscopic effect is that it will have spin drift.

The comment on B.
Bullet looses the speed with distance. So continuous wind will push the bullet more to side with distance. (function of drift with conitnuos wind is not linear)

 

[BourbonTrail]

I recommend Robert L. McCoy’s Modern Exterior Ballistics. I will grab some insights from my copy and post them later.

 

[Lone Star Bluegrass]

Here is the question:
Both bullets are fired into wind that is blowing perpendicular to direction of fire. but it is only blowing for a short distance. The remainder of the distance to the target the air is calm. there are two answers. The bullet on the left is "drifted" by the wind but maintains it's course- when the wind stops it continues effectively parallel to the line of sight.
the bullet on the right is affected by the wind by changing it's direction. Initially the bullet path is similar to the bullet on the left, but since it's direction wa changed by the wind, when the wind stops, the bullet continues on a path that is at an angle to the line of sight.
Options are left, right, neither.

View attachment 526792

It’s more similar to the diagram on the right. Once the flight of the bullet has been “pushed” it continues on that path.
See also Newton’s first law.

 

[fourfive8]

Yep, spin drift is a phenomenon separate from wind drift. Some early rifle sights had staffs regulated to compensate for bullet spin drift- the Buffngton sight as found on some later Trapdoor Springfields comes mind. I don't believe a cross wind causes the bullet's axis of spin to change direction. That would require violating some laws of physics- like gyroscopic angular momentum.... The bullet will remain pointed in the same direction while traveling through a crosswind. It is simply shoved laterally, the amount depending on vector, velocity of wind and duration of the lateral force. If it passes through the zone of a cross wind and re-enters calm air, its rotational axis is still pointed the same direction as when it entered the zone, having been shoved over commensurate with the amount of force exerted upon it while it was traveling through it. That's the way I visualize it anyway.