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Author Topic: Simple adjustment for wind drift ?  (Read 1875 times)

Offline Magnum_Willys

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Simple adjustment for wind drift ?
« on: April 06, 2017, 12:43:06 PM »
Have seen guys prefer Mil scopes for wind drift correction as the mils correlate better for adjustments?  Played around with Hornady Ballistic calculator to see what I could do with my moa scope for quick and dirty estimate to double check more sophisticated methods.

Turns out that just one click for every 100 yards after the first 100 is perfect for a 10 mph wind with my setup.  Can it be this easy ?  ( yea I know elevation/weather conditions will change things but probably not more than my wind estimates ?)

i.e. - 600 yards turn 5 clicks to adjust for 10mph cross wind. 



      

Offline kentrek

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Re: Simple adjustment for wind drift ?
« Reply #1 on: April 06, 2017, 01:05:45 PM »
It'd be that easy if you only ever had a perfect 10 mph wind  :chuckle:

Offline Bob33

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Re: Simple adjustment for wind drift ?
« Reply #2 on: April 06, 2017, 01:15:19 PM »
If the drift values are in inches, they look low to me.
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Offline Magnum_Willys

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Re: Simple adjustment for wind drift ?
« Reply #3 on: April 06, 2017, 01:55:02 PM »
If the drift values are in inches, they look low to me.

Thank you Bob ! You are right, I had selected G7 in the calculator instead of G1.  arghhh

Doesn't look near as sexy when you put the right numbers in  :bash:

« Last Edit: April 06, 2017, 03:00:16 PM by Magnum_Willys »

Offline Yondering

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Re: Simple adjustment for wind drift ?
« Reply #4 on: April 06, 2017, 05:48:31 PM »
If the drift values are in inches, they look low to me.

Thank you Bob ! You are right, I had selected G7 in the calculator instead of G1.  arghhh

Doesn't look near as sexy when you put the right numbers in  :bash:

If you play with the wind values, you can find a specific wind speed for your load and location that works with what you're trying to do out to 600-800 yards. Beyond that the wind drift starts to decay more and you'll have to add more correction.

I forget what it's called, but this is a technique some precision shooters use. For example, if I know my load needs 1 click per hundred yards in a 3 mph wind, I can factor that by the actual wind reading to easily get a quick wind dope. Say it's 400 yards and a 9mph wind, I'll need 12 clicks.

This is approximate of course, but can be close enough in the medium distances to work well.

Offline Reidus

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Re: Simple adjustment for wind drift ?
« Reply #5 on: April 06, 2017, 06:32:06 PM »
Put the data in excel and make a graph. Add a line of best fit and see if excel can come up with an equation. Maybe you can dumb the equation down to something simple.


Offline Yondering

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Re: Simple adjustment for wind drift ?
« Reply #6 on: April 07, 2017, 09:53:36 AM »
No need to use excel, just play with wind values in your ballistics app.

Magnum_Willys - I made some assumptions about your load and environmentals, but this should work as an example of what I'm talking about. I used: .338 300gr SMK @ 2850fps, G7 .3824, 330ft altitude, 50* F, 30.0586 in. HG.

Experimenting with wind values, 6 mph wind predicts 1 click (1/4 MOA) out to ~600 yards. Past that you need more clicks, 800 yards needs 9 clicks for example.

If all that is correct and proves out in the field, make yourself a chart based on 1 click /100 and 6 mph wind. Then any actual wind calculations are a factor of that value; 9mph wind for example will be 1.5 clicks /100.

Hope that helps!

Offline Reidus

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Re: Simple adjustment for wind drift ?
« Reply #7 on: April 07, 2017, 07:37:03 PM »
Here's an image that shows what wind drift looks like in a 10mph crosswind. All calibers/bullets will have a similar curve.

http://www.accurateshooter.com/cartridge-guides/243win/

Edit: the chart refers to drift in inches rather than MOA which is what you're using to dial your scope so I believe that would make the curve flatter.
« Last Edit: April 07, 2017, 07:42:36 PM by Reidus »

Offline Stein

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Re: Simple adjustment for wind drift ?
« Reply #8 on: April 07, 2017, 07:40:18 PM »
Yeah, it isn't the clicking that is hard, it is the precision estimating of wind over long complex terrain that is the challenge.  Whip your phone out of your pocket and in four seconds you have the exact calculations done.

Offline Reidus

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Re: Simple adjustment for wind drift ?
« Reply #9 on: April 07, 2017, 07:46:13 PM »
Or just go with the a zeiss rapid z reticle( Or something similar) that has the hash marks for 10mph wind at each yardage.

Offline SilkOnTheWetSide

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Simple adjustment for wind drift ?
« Reply #10 on: April 07, 2017, 07:47:49 PM »
Here's an image that shows what wind drift looks like in a 10mph crosswind. All calibers/bullets will have a similar curve.

http://www.accurateshooter.com/cartridge-guides/243win/

Edit: the chart refers to drift in inches rather than MOA which is what you're using to dial your scope so I believe that would make the curve flatter.

Man that's some crazy drift!

My 28 only drifts 44" @ 1000 yards. Just over a MIL.

Also, IMO you should hold for wind, not dial...


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Offline Magnum_Willys

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Re: Simple adjustment for wind drift ?
« Reply #11 on: April 20, 2017, 08:33:33 AM »
No need to use excel, just play with wind values in your ballistics app.

Magnum_Willys - I made some assumptions about your load and environmentals, but this should work as an example of what I'm talking about. I used: .338 300gr SMK @ 2850fps, G7 .3824, 330ft altitude, 50* F, 30.0586 in. HG.

Experimenting with wind values, 6 mph wind predicts 1 click (1/4 MOA) out to ~600 yards. Past that you need more clicks, 800 yards needs 9 clicks for example.

If all that is correct and proves out in the field, make yourself a chart based on 1 click /100 and 6 mph wind. Then any actual wind calculations are a factor of that value; 9mph wind for example will be 1.5 clicks /100.

Hope that helps!


Good idea, i didnt think of using wind multiples other than 10mph. That opens up some possibilities.   

Offline Bill W

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Re: Simple adjustment for wind drift ?
« Reply #12 on: April 20, 2017, 09:06:56 AM »
Better have your windage turret marked for the actual zero.  Otherwise you won't be able to tell what the "non wind" zero is.    My personal preference now is holding off for wind.  I was shooting in my first nationals in 2006 and I had the windage built into my sight corrections so I could hold closer to the x ring.   The wind was approximately 20 mph and then it reversed.   I went to the sighter to see what my new zero was and the combination of the new wind direction and the correction in my scope "blew" the bullet off the target.   I had an eventful couple of minutes until the wind came back to the original direction.

Offline Magnum_Willys

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Re: Simple adjustment for wind drift ?
« Reply #13 on: April 20, 2017, 09:22:05 AM »
Yea my inclination would be to dial close and hold for small variations. I can see how a big change would mess you up!

Offline high country

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Re: Simple adjustment for wind drift ?
« Reply #14 on: April 21, 2017, 08:23:12 AM »
Better have your windage turret marked for the actual zero.  Otherwise you won't be able to tell what the "non wind" zero is.    My personal preference now is holding off for wind.  I was shooting in my first nationals in 2006 and I had the windage built into my sight corrections so I could hold closer to the x ring.   The wind was approximately 20 mph and then it reversed.   I went to the sighter to see what my new zero was and the combination of the new wind direction and the correction in my scope "blew" the bullet off the target.   I had an eventful couple of minutes until the wind came back to the original direction.

Agreed. I got burned by a failure to RTZ on the windage too. Now I'm straight up hold for wind. If I need more than a mil or two......I need to reposition due to my own ethics.

Offline follow maggie

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Re: Simple adjustment for wind drift ?
« Reply #15 on: April 21, 2017, 09:01:03 AM »
I'm pretty simple. If the wind is blowing to bend the grass, I hold into it about 2". If the wind isn't bending the grass I just hold dead on. I've never shot an animal more than woo yards, so this has always worked great for me.

Offline Yondering

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Re: Simple adjustment for wind drift ?
« Reply #16 on: April 21, 2017, 10:01:47 AM »
Better have your windage turret marked for the actual zero.  Otherwise you won't be able to tell what the "non wind" zero is.   

I'm not sure I understand what the advice here is for, as it seems painfully obvious so I must be missing something. Do your turrets not have zero marks on them? And do you not set initial zero in no-wind situations?

All of my turrets have zero marks, and the turrets are reset to those marks after zeroing the rifle.

I prefer to hold in the wind too, my example above was for simplicity for the OP.

Offline Miles

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Re: Simple adjustment for wind drift ?
« Reply #17 on: April 21, 2017, 10:17:27 AM »
Turrets...where's all the fun in that?  I've got the simplest windage and elevation adjustments.  It's called hold over, compensate for wind, and pray.   Maybe not the best, but as the title requests, it's simple.




In all seriousness, turrets are in my near future. 

Offline jay.sharkbait

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Re: Simple adjustment for wind drift ?
« Reply #18 on: April 24, 2017, 05:42:58 PM »
I think wind calls are too dynamic to dial.

Taking your head out of the rifle ( physically and mentally) takes too much time.


Offline SilkOnTheWetSide

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Re: Simple adjustment for wind drift ?
« Reply #19 on: April 24, 2017, 07:42:32 PM »
I think wind calls are too dynamic to dial.

Taking your head out of the rifle ( physically and mentally) takes too much time.

Not to mention I've seen wind go from 1 MIL-2, back to 1.5 and steady on 1.

Can you imagine the ridiculousness of jumping in and out to make adjustments?

I set my wind to 10, it's linear. If you have a 1 MIL hold and the wind is 5 MPH, it becomes a .5 MIL hold.  Additionally if it's a 45 degree wind, it's a .25 MIL hold.

See! Wind is easy!


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Offline Bill W

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Re: Simple adjustment for wind drift ?
« Reply #20 on: April 25, 2017, 10:46:36 AM »
on the side winds.... how do you factor in whether the side wind is causing the bullet to rotate up.... or down if it's from the other direction?

I remember when wind was simple, just hold off a touch.  But then when the desire was to hit the bullseye dead center, reading the wind got a lot harder.    I shoot cast bullets out of a .30 BR and because of the lower velocity of lead bullets and poorer ballistic coefficient reading the wind is a graduate level course.   I shot one winter with the jacket bullet crowd as i thought they had a better handle on evaluating wind flags and found out that jacketed bullets were so much easier to shoot accurately.  The BC is so much higher and the velocity is at least 1200 fps faster.

But in a cross wind and depending on which way the twist in the barrel is, the bullets either rise up somewhat, or are pushed down based on wind direction.

Offline high country

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Re: Simple adjustment for wind drift ?
« Reply #21 on: April 25, 2017, 11:44:56 AM »
on the side winds.... how do you factor in whether the side wind is causing the bullet to rotate up.... or down if it's from the other direction?

I remember when wind was simple, just hold off a touch.  But then when the desire was to hit the bullseye dead center, reading the wind got a lot harder.    I shoot cast bullets out of a .30 BR and because of the lower velocity of lead bullets and poorer ballistic coefficient reading the wind is a graduate level course.   I shot one winter with the jacket bullet crowd as i thought they had a better handle on evaluating wind flags and found out that jacketed bullets were so much easier to shoot accurately.  The BC is so much higher and the velocity is at least 1200 fps faster.

But in a cross wind and depending on which way the twist in the barrel is, the bullets either rise up somewhat, or are pushed down based on wind direction.

The values and math are the same, just the method of horizontal compensation changes. I still run the numbers, but instead of holding zero and making a .7 mil corrrection it's in the scope. You either have to be a memory master, or have a ballistic solver handy.

Offline Bill W

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Re: Simple adjustment for wind drift ?
« Reply #22 on: April 25, 2017, 01:28:42 PM »
on the side winds.... how do you factor in whether the side wind is causing the bullet to rotate up.... or down if it's from the other direction?

I remember when wind was simple, just hold off a touch.  But then when the desire was to hit the bullseye dead center, reading the wind got a lot harder.    I shoot cast bullets out of a .30 BR and because of the lower velocity of lead bullets and poorer ballistic coefficient reading the wind is a graduate level course.   I shot one winter with the jacket bullet crowd as i thought they had a better handle on evaluating wind flags and found out that jacketed bullets were so much easier to shoot accurately.  The BC is so much higher and the velocity is at least 1200 fps faster.

But in a cross wind and depending on which way the twist in the barrel is, the bullets either rise up somewhat, or are pushed down based on wind direction.

The values and math are the same, just the method of horizontal compensation changes. I still run the numbers, but instead of holding zero and making a .7 mil corrrection it's in the scope. You either have to be a memory master, or have a ballistic solver handy.


I wondered if you long range jacketed bullet shooters knew about this.   It needs to be factored in if one is trying for a dead center or "pinwheel" bullseye.     Depending on which way the rifling goes and which way the wind is blowing the bullet is either pushed up/or down in a side wind.

Did a search on external ballistics and came up with another on head/tail winds.    This made me pull out hair at times during matches as the degree of difficulty is about 10 time more when shooting cast bullet benchrest.   Here's the info below.

Magnus effect[edit]

The Magnus effect. V represents the wind, the arrow F is the resulting Magnus force towards the side of lower pressure.
Spin stabilized projectiles are affected by the Magnus effect, whereby the spin of the bullet creates a force acting either up or down, perpendicular to the sideways vector of the wind. In the simple case of horizontal wind, and a right hand (clockwise) direction of rotation, the Magnus effect induced pressure differences around the bullet cause a downward (wind from the right) or upward (wind from the left) force viewed from the point of firing to act on the projectile, affecting its point of impact.[60] The vertical deflection value tends to be small in comparison with the horizontal wind induced deflection component, but it may nevertheless be significant in winds that exceed 4 m/s (14.4 km/h or 9 mph).

Magnus effect and bullet stability[edit]
The Magnus effect has a significant role in bullet stability because the Magnus force does not act upon the bullet's center of gravity, but the center of pressure affecting the yaw of the bullet. The Magnus effect will act as a destabilizing force on any bullet with a center of pressure located ahead of the center of gravity, while conversely acting as a stabilizing force on any bullet with the center of pressure located behind the center of gravity. The location of the center of pressure depends on the flow field structure, in other words, depending on whether the bullet is in supersonic, transonic or subsonic flight. What this means in practice depends on the shape and other attributes of the bullet, in any case the Magnus force greatly affects stability because it tries to "twist" the bullet along its flight path.[61][62]

Paradoxically, very-low-drag bullets due to their length have a tendency to exhibit greater Magnus destabilizing errors because they have a greater surface area to present to the oncoming air they are travelling through, thereby reducing their aerodynamic efficiency. This subtle effect is one of the reasons why a calculated Cd or BC based on shape and sectional density is of limited use.

Poisson effect[edit]
Another minor cause of drift, which depends on the nose of the projectile being above the trajectory, is the Poisson Effect. This, if it occurs at all, acts in the same direction as the gyroscopic drift and is even less important than the Magnus effect. It supposes that the uptilted nose of the projectile causes an air cushion to build up underneath it. It further supposes that there is an increase of friction between this cushion and the projectile so that the latter, with its spin, will tend to roll off the cushion and move sideways.

This simple explanation is quite popular. There is, however, no evidence to show that increased pressure means increased friction and unless this is so, there can be no effect. Even if it does exist it must be quite insignificant compared with the gyroscopic and Coriolis drifts.

Both the Poisson and Magnus Effects will reverse their directions of drift if the nose falls below the trajectory. When the nose is off to one side, as in equilibrium yaw, these effects will make minute alterations in range.

Offline Henrydog

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Re: Simple adjustment for wind drift ?
« Reply #23 on: April 25, 2017, 01:49:42 PM »
There is also the Coriolis effect.  In the Northern Hemisphere the longer the object is in flight the more off to the right it will be at the target.  Same reason all toilets flush clockwise.  Just the reverse in the Southern Hemisphere.  The French Military noticed it when artillery improved in the mid 1830's.   

I've never noticed it when shooting my 45/70 with open sites :chuckle:

Offline Miles

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Re: Simple adjustment for wind drift ?
« Reply #24 on: April 25, 2017, 03:09:03 PM »
You guys are overthinking things...

 

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