Wind deflection vs. displacement

[cody c]

I heard an interesting thing the other day that got me thinking, someone who has been shooting a lot longer then I said something to the matter of, if you have wind closer to you when you shoot as opposed to further from your target it makes more of a span from point of aim, basically he introduced the idea that I should consider two variables.

1. The wind displaces the POI of your projectile, fairly simple math that would involve the time your bullet is in flight and the average wind speed over the distance traveled, or if there was a channel of wind along the flight path you could figure the time it traveled through that channel and speed of wind through that channel, i.e. a simple side step on the journey but the compass direction would remain the same.

2. The angle at which the projectile is traveling could be deflected, as a pool ball grazing against the side of the table would have its direction changed, this would have a greater impact on POI.

I assume both factors come into play in some degree, but its a concept that's new to me and would affect the math of POI greatly, more so on the second point, what do you fellas who no more know about this? Do you account for the latter?

 

[Sherlock Gnomes]

Wind pushing cross ways at muzzle means greater spread further out.

 

[Shooter ----/]

I'm interested to hear others opinions on this. I have my own ideas on this but nowhere near the trigger time nor scientific mindfulness to prove or disprove my thoughts.

 

[Shibby!]

True.

Wind at shooter affects trajectory more so than wind down range.

While the bullet is travelling faster, it's entire flight path is altered, vs just minor deviations at the target.

With that said, my experiences have proved that it doesn't matter either way. You have to account for the WHOLE trajectory.

Getting a wind meter will prove this quickly. You can gauge all the wind you want at trigger time, if you aren't taking readings (visual,etc) downrange, you're wasting your time. Especially shooting in the foothills where wind can be completely opposite of shooter location.

 

[Sherlock Gnomes]

True.

Wind at shooter affects trajectory more so than wind down range.

While the bullet is travelling faster, it's entire flight path is altered, vs just minor deviations at the target.

With that said, my experiences have proved that it doesn't matter either way. You have to account for the WHOLE trajectory.

Getting a wind meter will prove this quickly. You can gauge all the wind you want at trigger time, if you aren't taking readings (visual,etc) downrange, you're wasting your time. Especially shooting in the foothills where wind can be completely opposite of shooter location.

This ^^^^^^^ well said

 

[Gunneegoogoo]

Your thoughts and questions are not wrong at all. It's grossly overthinking it, but I'm certainly not one to be able to criticize that!!!

Air behaves as a liquid, therefore it is in a way, an object, like the pool ball you mention. So, when the bullet encounters a new "wind zone" it will indeed be deflected to some degree - just like an aircraft getting bounced around in turbulence.

The effect of this has absolutely no practical method of measuring or predicting. Even if you had a wifi kestrel every 25 yards feeding info on your entire flight path into your ipad on the shooting bench, you'd then have to account for the vectors effecting the bullet as it passes through each wind "zone" while its nose-up/nose down attitude changes throughout it's course. Sounds like supercomputer type stuff to me!!

I wonder if there are any guys/girls with artillery experience on here?? They could inform us what factors they look at when setting the angles of those big guns.

In LR rifle shooting, I'm pretty confident in saying this concern is on the "art side" of the line between science and art. You calculate everything you can, make your adjustments, use the best shooting technique you can, watch where your bullet lands - and adjust to make it right..... Again - great to think about, but likely not reasonable factors to consider in reality.

-J.

 

[cody c]

You may be right about it being a very small factor, but the again so is calculating the spin of the earth, humidity of the air and altitude to calculate density, and those factors are calculated by shooters, they may be the elite and work in the Middle East and have needs beyond ours but I find the math and physics interesting regardless.

 

[Mystic Precision]

Glad to see those understanding that wind is far from linear and terrain plays a major role to the air your bullet actually sees.

The wind to pay most attention to is the wind that affects your bullet the most... It is where ever it is and will not stay there on a constant basis. That is why artillery call it a firing SOLUTION... you add up all the lefts and rights, ups and downs and get the final "guess".

The only place I have seen the close wind/far wind argument work is in Sasketchewan and Winnipeg... Anywhere that is a wide open flat range. I also shoot in the hills and winds come from every direction and in every axis so you better start understanding what the real affect is likely to be.

Also, understand that air moves in layers so the air you see may not be the air the bullet travels through... better start learning to read mirage. Around here, no problem seeing ground air going one way and air a hundred feet up going the other. Direction and velocity is not always constant with altitude.

So.... let's add more confusion. Current trend in bullet designs to improve BC also create another massive variable... how this shape responds to cross wind vectors through its travel to distance. Twist rate and velocity at distance have profound affects on this as will the actual shape of the bullet.

You better read up on dynamic and static balance/stability... also, supersonic vs transonic balance and turbulance.... and of course, wonky stuff like aerodynamic jump.

Confused, you should be. How to calculate? You don't.... not in the smartphone, hit a few buttons kind of way. Only shooting and plotting the impacts are going to help you get a handle on this.

All that glitters..... the process of using an "optimal" twist to reach a mathematical SG number, may also be leading to less then optimal accuracy at distance.

Test, test, and test some more... Beats trying to figure out the math.. And the more you test, the less you will worry about the numbers which don't always tell you the real world result

Have fun....

Jerry

 

[Glock4ever]

This is a bit of an oversimplification. Not wrong but not necessarily right either. Wind is one of many factors to consider when you shoot but like other factors it is relative to the velocity of your projectile, the ballistic co-efficient, the distance you are shooting, etc. Can wind cause more deflection near the muzzle than compared to downrange? Answer is yes - it is possible but it is no different than stating that if you have no wind at muzzle and a lot of x-wind near the target it will be deflected off the POA. Stating this as some sort of rule/consideration that is any more important that other factors is incorrect. Good shooters can read wind both near and far by looking at environmental conditions and coming up with a "wind call" a wind call shouldn't be made solely on the wind at muzzle or at target but as a combination of both. If you watch benchrest shooting you will note that there are flags place at differing ranges to help facilitate the shooter in making a wind call. So here is an example of how a wind call can be made:

You are shooting at 600m with a .308 Win 155 grain Scenar at 2800 FPS on a 24 C day, 840hPa, with varying wind conditions. After having shot a lot and keeping a nice log - you have developed a bunch of information regarding how your round travels in specific conditions (an excellent tool to help you shoot better BTW). So you look at the flags on your range and you note that:

At 0-200m the wind appears to be a 2m/s wind (full value left to right)
From 2-400m (half value left to right)
From 4-600m (zero value possible tail wind)

You decide that the wind from 15 kph is most likely going to cause the most deflection (nearest to you) and compensate 0.6 Mils left to shoot into the wind. Very likely you will not hit exactly but the wind call will give you a decent start point to correct your shot. It is also the reason why many BR shooters will try to wait for the wind to completely die down and give them the best opportunity to hit exactly where they want.

Likewise you could have a zero value wind near you and a full value x-wind closer to target which you may need to compensate for. Hopefully this is useful... As for the question about how artillery does the computations. While the priniciples of artillery shooting are applicable to LR small arms shooting, many of the factors that are considered when shooting say 40km are just not worth considering when you are shooting small arms. As an example, coriolis, spin drift and met is much more important consideration at 40 km than it will be at only 1 km - this is something best explained with a whiteboard/verbally than what would be contained in a post.

 

[SND]

First wind it sees will start to take the bullet one way, then it wants to keep going that way, others winds will either add or subtract to that.
As the wind changes the bullet doesn't instantly go with it, inertia/momentum. Its all curves.
Where it ends up, an experienced guess at the right time is as good(or better) than any math for our use.

 

[Gunneegoogoo]

You may be right about it being a very small factor, but the again so is calculating the spin of the earth, humidity of the air and altitude to calculate density, and those factors are calculated by shooters, they may be the elite and work in the Middle East and have needs beyond ours but I find the math and physics interesting regardless.

No, those calculations make quite a difference (Coriolus is about 4" at 1000yds) and are just as important to you and me shooting paper and steel as it is in the sand by the pros.

I don't want to discourage you, the fact that you asked means you're thinking which is great.

Humidity, wind at the tip of your barrel, temp, coriolis, spin drift, drop, etc are all things easily attained and allowed for - and they should be. That's the science. Reading wind down range, mirage, light, etc is the "art".

-J.

 

[cody c]

Ok, good posts here fellas, especially from Jerry, glocks4ever and gunneegoogo, thanks for taking the time to chime in.

I'm getting the sense now that correcting for wind is much much more an art then a calculation, I can kind of visualize myself adjusting focus from near to far trying to read mirage long the way, and using my right hand pointed forwards, then shifting left or right as per wind drifts along the way to try and get an overall average guess as to what kind of overall adjustment would be (if that makes any sense) .

SND, just to be clear, the two points I'm talking about in a different and silly analogy:

Bubba decides to row his boat across the river, he moves across pointed west wards the entire route, the river shifts him down stream as he crosses, in some areas the current is faster and he moves downstream faster but still pointed west, his path looks pretty much like a straight line though on a diagonal.

Scenario two, Bubba's brother Dougie is head across the river, as he heads in the current catches the tip of his boat and changes the direction from west to slightly down stream of west, as he continues the river continues to pull the bow downstream ever so slightly as he continues to cross, perhaps mostly when he hits faster current, his path of travel is more of an arch and theoretically he ends up further down stream of Bubba.

If you caught what I was trying to explain before this stupid analogy I mean no disrespect of course, and when Bubba finds Dougie they will probably get drunk on moonshine and proceed to hack up a barrel of grandpas unissued Enfields with a crooked hacksaw to lighten them up so it all kinda works out in the end anyways!

Typed with my thumbs from the Saskatchewan airport.

 

[Gunneegoogoo]

Bubba can correct the heading of the bow of his skiff via paddling.....a bullet can't. Once it leave the barrel it's at the mercy of external factors only.

Dougie just sounds too drunk to sort it out!!!

Typed from a meeting room in Regina, wishing for my own death.

 

[Juster]

One factor is that the bullet is travelling more slowly at longer range, which increases wind deflection. Plus wind gradient with increasing trajectory.

 

[Mystic Precision]

...

Bubba decides to row his boat across the river, he moves across pointed west wards the entire route, the river shifts him down stream as he crosses, in some areas the current is faster and he moves downstream faster but still pointed west, his path looks pretty much like a straight line though on a diagonal.

Scenario two, Bubba's brother Dougie is head across the river, as he heads in the current catches the tip of his boat and changes the direction from west to slightly down stream of west, as he continues the river continues to pull the bow downstream ever so slightly as he continues to cross, perhaps mostly when he hits faster current, his path of travel is more of an arch and theoretically he ends up further down stream of Bubba.

And this is what I am refering to with "new gen" bullets. The affect of yaw wrt to cross winds can vary depending on the bullets, RPM and velocity. It can create some very interesting results on target.

Keep on this when you are testing this shooting season... Try and plot on target and compare to various winds intensity and direction.

If you have an accurate rifle and load and consistent in your shooting, you might just see some interesting results.

YMMV

Jerry

 

[swissinn]

All you can do is plug in the knowns. The simple answer is that experience counts for a ton more than your PDA spits out. Just be accurate with your inputs so you get the best data out.

 

[Mystic Precision]

And don't get hung up that the LCD screen doesn't agree with the target.

There are many variables the software simply cannot account for... including the shooter.

Use data as a guide... let the target tell you the "truth".

Jerry

 

[Leeper]

I have always said, if my first shot is a "V", I'm likely to have a good day. If my first shot is a 4 I'm probably starting into a long day. Most of my days are long. With that out of the way, I'll tell you what little I have learned. I have not see any real evidence that the close-up wind is of any greater importance. While I will try and utilize mirage when I can, it is seldom that it tells me what is really going on. When I am able to shoot well by watching mirage, it is only because the mirage is, on that day, a decent indicator. Mirage is of more value, by far, in the mountains than on the flatlands. If you are going to try and use mirage as a wind flag, you had better have a spotting scope focused about halfway out and ten feet above the line of sight (if shooting at nine hundred). This assumes you have a background against which the mirage can be seen. Looking at the sky, a good way to spot birds, isn't much good for gauging wind. Wh
When at an unfamiliar range, it is critical to get an idea of what wind flag patterns are likely to be showing you. This is where record keeping (on paper or in your head) comes into play. It is better to have an idea regarding these patterns before you start shooting. I try to spend some time just looking downrange before the shooting starts and I really want my fouler to be a good shot. I pay close attention to relays in which I am not shooting.
The one thing I have found to be constant is that every day is different and what happened yesterday may or may not be worth remembering.

 

[Gunneegoogoo]

One factor is that the bullet is travelling more slowly at longer range, which increases wind deflection. Plus wind gradient with increasing trajectory.

It's travelling slower at longer range yes, but a 1degree deflection with 100yds to travel to the target has less effect than a 1degree deflection right out of the barrel.....

SO MANY VARIABLES!!!!

 

[Shibby!]

It's travelling slower at longer range yes, but a 1degree deflection with 100yds to travel to the target has less effect than a 1degree deflection right out of the barrel.....

SO MANY VARIABLES!!!!

Correct.

Jerry,

Are there any tactics you use to gauge wind when shooting over valleys?

My issue is confusion begins because I measure wind when shooting (Kestrel), and gauge wind by grass, flags, or trees at target. Over the valley is an unknown. As you mentioned, the velocity and direction of wind can change in this area (including up and down drafts), as well as air density. Due to it's height above ground there is no mirage. Valley height averages 50-~300y and distances is 550y. We shoot from an elevated platform. Closest target is 640y.

I'm always jealous of people who get to shoot in flat fields. The mountains sure make things tricky.