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Thoughts on wind angle.....

 
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  #1  
Old 02-11-2005, 10:32 PM
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Thoughts on wind angle.....

I was setting around the house today, wishing the wind were a bit more stable so I could go shoot a few more groups before the rain sets in tomorrow, when I started thinking.
Ive been shooting at my portable target stand for a couple months now at 1350Yds. It is pointed almost due north out of nececcity, which also happens to be the direction the wind either blows from, or to here in Oklahoma 99.99% of the time. Needless to say, I shoot in a lot of those wonderful "fishtail" winds that switch back and forth from 10-15 degrees left to right, requiring you to switch compensation back and forth in both directions.
And then something dangerous began to happen, my mind began to wander...
Of fixed target ranges, you are pretty much at the mercy of the wind, but obviously you would position yourself for the optimal wind angle if you were hunting long range. My question is what would you consider to be the "optimal angle"
I wipped up a table for comparison in some of that free time today. It goes something like this... all values in IN.

The question is would you want to:
shoot into/out of the wind for minimal sensitivity to different windspeeds,
shoot in a full value crosswind for minimal variance in amount of drift due to varying angle of wind,
or something in between. Just looking at the book data, it would seem that the effects are most balanced for a 40 degree angle wind... at least at 10mph.
Lets hear it, how do you want your wind if you can pick?
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Old 02-12-2005, 07:14 AM
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Re: Thoughts on wind angle.....

I find that I can do a better job of estimating the winds directions, and averageing them together, than I can estimate the various wind speeds and figuring out a composite value to use. I guess I just have an easier time visualizing how it is going to change directions as it flows over the ground contour, but those gusts give me fits. Thus I prefer the straight on head wind.

I guess a constant velocity wind that doesn't shift direction would be too much to ask for and would take most of the frustration out of the game! [img]/ubbthreads/images/graemlins/laugh.gif[/img]
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Old 02-12-2005, 01:29 PM
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Re: Thoughts on wind angle.....

My preferance has been towards the "head on" wind as well, but these fishtail winds have been killing me lately. My shooting seems to support the data I generated, in that, a 5 degree shift, right and left during the course of shooting a group leaves you with a 20"+ group (in10mph@1350)
Annoying to say the least.
Most of the terrain my bullet passes over is about 50-70ft below line of sight, and the air speed tends to be very stable. Kinda precludes windflags though.
At either extreme angle, blowing the wind by 1mph, and 5 degrees wins you a 1 foot miss.
Any other long range hunters want to chime in?
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Old 02-12-2005, 02:48 PM
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Re: Thoughts on wind angle.....

Abinok,
Great topic - wind speed and direction are the challenges we all face. I just use the simple full-value/partial value chart taken from military instruction manuals. Your chart refines this greatly, very interesting.
Personally I enjoy the challenge of fish-tails, they keep the spotter on his toes big time. Hunting in them is another thing from clanging steel tho. Hopefully we will get more response, this is key issue with LR shooters. Big problem for me is that I have not shot long for a couple of months - have to get back into the mode each spring. Great info, thanks.
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Old 02-12-2005, 04:35 PM
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Re: Thoughts on wind angle.....

I too have a range that I shoot at which the prevailing wind is at my 12 or 6 O'Clock, between 10-2 or 8-4 really.

It makes for some frustrating observations & calculations on each shot for sure.

I've shot with the predominant wind near 90 degrees a whole bunch as well, and though it's a bunch different, if you can measure wind speed, have a bit of mirage to read, I believe it's easier to keep first round hits closer to POA, and definitely easier to keep group size down. Of course, if the wind is very steady at say 11 O'Clock and been that way for some time and you let a few fly for group, that's pretty easy going as well. Miss a switch to 1 O'Clock and you'll be wondering what happened.

Mostly when I hunt, make that hunt at long range, I'm looking for favorable wind conditions (read low intensity with a predictable and predominant vector) so I can set up near 90 degrees to it so wind speed is all I'm really dealing with in most cases.

In a low wind speed (2-7 or so mph) it's much more forgiving if you miss the actual full value wind speed number you need to dial a correction for, especially if it's under 2-5 mph.

You will also miss by much less with a 90 degree crosswind at 1350 yds verses a 0 degree component if you misread conditions, if you consider that windspeed is fairly easy to see/judge/attach a number to than is a crosswind change in small degrees.


In your example at 1350 yds, for every 1 degree you miss a crosswind change by, POI would be off by 11.5". So, we know that every one minute on a clock dial face is equal to 6 degrees, therefore if the wind vector changed from 12 O'Clock and went to 12:02 (2 minutes after 12), which by the way is a very small change to detect, very small, you would be a total of 12 degrees in error... or 12 x 11.5" per degree = 138 inches error in POI.

In a 90 degree crosswind, you can see that the same 12 degree error from a wind vector change is just 4" POI error, roughly.

To even equal the whoppin 138" of error by missing a wind speed change here that the 12 degree wind vector change caused in the headwind situation above, you would have to miss a wind speed change by about 10.6 MPH. (138" divided by 13 inches per 1 MPH = 10.6 MPH.) Therefore, if the prevailing wind speed was measured at 10 MPH, wind speed would have to be less than 0 MPH in order to equal the error produced of 138".

Do you think you'd notice if wind went to 6-7 MPH from 10 MPH? I think you'd definitely notice it... I'd bet my life on it you would if wind dropped to "anywhere" near zero.

Another thing illistrated here is, you can definitely see there is no room for error at 1350 yards if you plan on a first round hit on a realistic Elk/Moose size kill zone.

You may however see which might lend itself better to a closer POI at whatever range, target shooting or hunting.
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Old 02-13-2005, 04:29 PM
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Re: Thoughts on wind angle.....

Ian, I will agree with you that the fishtails are challenging, and make a good spotter important, unfortunately I shoot without a spotter most of the time. The rifle im shooting only weighs 13.7 lbs, so it is almost impossible to spot your own hits. From a solid prone position it can be done, but youve got to be on your toes. TOF is about 2 sec. I used to use the deflection charts in the manuals as well, untill I realizd 2 things. since most of them are broken down into the "hours on a clock" format, you only have 4 referance angles. 0, 90, 30, and 60. As anybody can see, at 1350, the differance in those angles is huge. Once I realized that they were the product of the sine of the angle, I started getting firing solutions that were much more accurate. Anybody out there who wants to get a table like the one I made above, just use one of the ballistics programs on the market to get your inches/mph or moa/mph data, then multiply by the sine of the angle. Just make sure you have your calculator set to degrees, not radians.
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  #7  
Old 02-13-2005, 05:02 PM
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Re: Thoughts on wind angle.....

brent,
im glad to see somebody who leans toward the full value wind preferance. I guess I decided I had to post this topic since ive heard everybody say something like... "I only shoot when everything, including the wind is just right". Only problem is that the "perfect wind" is really more of a subjective thing, determined by whether the wind speed is steadier than the wind direction. I hope you were doing your math in your post from the data I provided, especially the referance to the 11.5" for 1 degree change. My chart was for 5 degree changes, which I think is really about the maximum level of precision somebody (ie...me) can get on direction in the field.
In the course of doing all this math intensive thinking (is that why my head hurts?) I think its very important for a shooter or hunter to know their limitation on accurately generating a firing solution for their "maximum range" and how important it is to have that maximum range at which you are willing to shoot in your head as an actual number, not just a zone between this yardage and that.. For my setup, 1350 has almost exactly 2x the wind correction I use at 1000yds for the same condition. This only reinforces the fact that stuff that worked at 400, don't work at 1000. Ditto for 1350 too.
More range means more precision in everything youve gotta do, theres just no way around it.
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