This question came up in another recent thread, but because (as I said there) it’s been debated for as long as I can remember going back decades I decided it was worthy of a separate discussion.

One idea is that wind that blows against a bullet during the first part of its flight will blow it off line more because the effects are caused immediately and persist for a longer distance.

The other idea is that wind blowing against a bullet near the end of its flight will have more effect because the bullet is traveling slower, and it’s true that slower bullets are affected more by wind drift than faster bullets of the same type.

As I also mentioned elsewhere, I recall that the respected ballistician Bryan Litz has said that early flight crosswinds affect bullets more than late flight winds. But other than arguing from authority, is there a way to answer the question?

I have never considered the problem before and it’s possible the following is wrong for some reason, so I’m interested in knowledgeable comments.

It occurred to me that the question could be answered in a certain limited situation by just comparing how much a wind would blow a bullet off course if it were at the beginning of the flight or at the end. To do that I used the Applied Ballistics (AB) solver to determine how much a .308 caliber 168 grain Sierra MatchKing bullet would be blown off course over a distance of 100 yards by a 10 mph full value crosswind at two different velocities.

A common velocity of 2700 fps was selected for the first 100 yard segment, and a velocity of 2096 fps for the start of a segment from 400 to 500 yards. (The 2096 is what AB told me the velocity would be at 400 yards under “standard” atmospheric conditions with a MV of 2700 fps.) For this discussion we’ll assume that the 10 mph wind blew on the bullet for exactly 100 yards of the near or far flight only, and then abruptly stopped.

According to the solver, the bullet would be blown off course by 0.61 inch from 0 to 100 yards with a MV of 2700 fps.
At a MV of 2096 fps, the windage effect would be 0.88". From that we could conclude that the lower starting velocity at the longer range of 400 yards would allow greater deflection with the same 10 mph crosswind—no?

No. What the first figure of 0.61 doesn’t address is the cumulative effect of having been blown off at an angle (~0.0097°) whose subtension increases throughout the flight. It’s blown off by 0.61" during the first 100 yards, but by the time it reaches 500 yards it will be off by about 3.05" even if the wind stops abruptly after the first 0.61" of deflection. On the other hand, the same wind that blows on the bullet during its last 100 yards at the lower initial velocity of 2096 fps will move the bullet only a total of 0.88".

My calculation assumes of course the unlikely condition that the wind blows the bullet off course for only 100 yards of travel. I believe, though, that the principles and effects are the same with a normal wind: Wind at the beginning of the bullet’s flight has more effect than at the end.

So what if the near wind blows from 0 to 250 yards then stops, and for the next shot the far wind suddenly starts at 250 and blows until the bullet reaches 500 yards.

AB says that in that situation from 0 to 250 yards the deflection would be 4.03", and continuing at that angle to 500 yards with no more wind would be a total deflection of 8.06".
AB also says that the velocity at 250 yards would be 2313 fps, so that’s the starting velocity for the segment from 250 to 500 yards. Using that MV, the total deflection would be 5.07" at 500 yards, or again less than the total deflection if the wind had been blowing during the first 250 yards.

These calculations were done with only one specific bullet and conditions. Could things be different if they were different? I doubt it, but the question is left as an exercise for the student.

What say the authorities? Make sense or have I overlooked some obvious factor that would change the outcome?

You pretty much naied it on the first try. The real question is what happens under switchback wind conditions.

quote:

Originally posted by SgtGold:
You pretty much naied it on the first try. The real question is what happens under switchback wind conditions.

I’m not sure what they’re called, but from time to time we hear about someone’s efforts to make an automated aiming system that’s supposed to eliminate the need for shooter skill. Identify and designate the target through the scope, pull the trigger, and: Hit.

What such systems cannot of course deal with are variable wind effects. If they could measure the wind at the shooter’s location that would help some in some situations, but I’m not aware of any that have figured out even that much—except maybe in fiction. There have been a few thriller novels supposedly written by former military snipers, and I remember one some years ago that featured an automatically aiming rifle that was capable of tracking and hitting a target bobbing around at random on a rough sea surface.

It's called EXACTO.

https://www.wearethemighty.com...guided-sniper-round/

quote:

Originally posted by sigfreund:

quote:

Originally posted by SgtGold:
You pretty much naied it on the first try. The real question is what happens under switchback wind conditions.

I’m not sure what they’re called, but from time to time we hear about someone’s efforts to make an automated aiming system that’s supposed to eliminate the need for shooter skill. Identify and designate the target through the scope, pull the trigger, and: Hit.

What such systems cannot of course deal with are variable wind effects. If they could measure the wind at the shooter’s location that would help some in some situations, but I’m not aware of any that have figured out even that much—except maybe in fiction. There have been a few thriller novels supposedly written by former military snipers, and I remember one some years ago that featured an automatically aiming rifle that was capable of tracking and hitting a target bobbing around at random on a rough sea surface.

quote:

Originally posted by SgtGold:
It's called EXACTO.

I vaguely recall seeing that and it would be the ultimate no-to-little skills required small arm, but not exactly what I was thinking of. It would be interesting to know how much capability the projectile has to hit targets moving quickly and erratically.

Something I ran across recently in a discussion about combat in Ukraine is the rise of laser detection and countermeasure systems. Although I’d never heard of them before, I gather that they’re not new and are even in US service. The Ukrainian sniper talking about them said that they don’t use laser rangefinders because of automatic systems that fire at the source almost instantly after detecting a laser paint.

It's indisputable that breaking wind before the trigger pull will have more effect on bullet flight path than breaking wind after the trigger pull.

quote:

Originally posted by parabellum:
It's indisputable that breaking wind before the trigger pull will have more effect on bullet flight path than breaking wind after the trigger pull.

May the wind at your back not be your own.

Here's a better video on the EXACTO bullet. There is not too much info out there.

https://www.msn.com/en-us/news...wWS?ocid=socialshare