Bullet Drift From Wind

[taliv]

we're not forgetting it. it was mentioned in post 21 and 23

thanks for the graph

 

[Walkalong]

Good post Bart, you said it much better than I did.

I have never done any charts, or done the math, but my experience in 100 and 200 yard Benchrest mirrors what Bart said. Bart shot (Still shoots?) long range at a high level for a long time and was around all the best shooters doing it as well. That kind of experience beats any math in my book.

And again, it is for reasonably constant wind along the path to the target. If it is blowing hard close to the shooter and lightly farther away, or blowing lightly close in and hard further away, it is different, and you have to base your hold (Or dialing off) on the wind where it is. But you still have to factor in that a 5 mph wind close to you makes more difference than a 5 mph wind near the target. People who are good at reading wind do all the math subconsciously in their head based on feel and experience.

 

[lysanderxiii]

This is not an accurate statement. Wind at the target has more effect on a bullet than wind closer to the rifle's muzzle. As the bullet flies, it loses speed and is more susceptible to bullet drift closer to the target where it has less speed to cut through the wind.

If I am reading that graph right the green line is for a wind acting from 0 to 333 yards and then stops, the red line is with the wind starting at 667 and stopping at 1000 yards.

The 10 mph wind during the first 333 yards of bullet travel has caused a drift of approximately 9".

The 10 mph wind during the last 333 yards of bullet travel has caused a drift almost double that of the first 333 yards.

When he says:

A given crosswind speed close to the rifle has more effect on downrange bullet drift than that same crosswind near the target.

He means the overall effect, not that the bullet is moved further when it is closer to the muzzle.

 

[Bart B.]

lysander, thanks for putting the icing on my drifty cake. Yes, your interpretation was better written than my explanation.

 

[Bart B.]

Here's my chart showing wind speeds above the line of sight:

[resize=1000] [/resize]

 

[taliv]

helpful tip: you can use the resize tag to fix giant graphics. e.g. put [resize=700 or some other number of pixels] then your [image tag] then close it with the [/resize ]

 

[Bart B.]

Thanks, Taliv, for the helpful tip. Did it.

Tried different sizes of images in my Flickr site but had to leave before I finished. That's the best way anyway.

Kudos to you for that.

 

[Walkalong]

lysander, thanks for putting the icing on my drifty cake. Yes, your interpretation was better written than my explanation.

Much better than I put it as well.

not to mention the fact that going offline early is magnified more and more as it moves away from that spot.

geometry

Or, once it is angled away early on, it continues to angle away all the way to the target. But lysander's explanation is still better.

 

[denton]

The mechanics of wind drift are actually different from what you might suppose. It is not a matter of wind blowing against the side of the bullet.

The bullet will orient itself so that it experiences minimum drag. The bullet will actually slightly nose into the wind, so that the streamlines flow directly from tip to base.

With the bullet turned a little into the wind, the drag vector no longer points back toward the firearm. It has a vector component to the side. It's that sideways vector component that moves the bullet left or right.

What that says is that windage is highly dependent on BC. Higher drag bullets will experience more sideways displacement.

 

[lysanderxiii]

Actually, all of the ballistic calculator programs just use the BC to calculate the drift.

Put any bullet caliber, weight, BC and Vm in a ballistic calculator then vary just the bullet weight.

The wind drift will remain constant.