Thoughts on wind angle.....

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by abinok, Feb 11, 2005.

  1. abinok

    abinok Writers Guild

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    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.
    [​IMG]
    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?
     
  2. RBrowning

    RBrowning Well-Known Member

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    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! /ubbthreads/images/graemlins/laugh.gif
     
  3. abinok

    abinok Writers Guild

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    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?
     
  4. Ian M

    Ian M Well-Known Member

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    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.
     
  5. Brent

    Brent Well-Known Member

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    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.
     
  6. abinok

    abinok Writers Guild

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    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.
     
  7. abinok

    abinok Writers Guild

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    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.
     
  8. Brent

    Brent Well-Known Member

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    Abinok,

    My mind has been on too many things here lately, not sure where it was when I looked at that but, wow did I get that all twisted up!!

    I didn’t even pay attention to the first column there, “drift”. Seems I was thinking something else on the second column even after reading it was 5 degrees. Went back to it and just had 1 degree in my head for some damn reason I forget….

    Anyway, you’re absolutely right. And to add to that, a 12 degree change in wind vector from a 90 degree crosswind is only 2”, not 4”….. Isn’t it?.... again, don’t ask me what I was thinking there either.

    138”??? Well, again, had I paid attention to the drift column….

    If anyone has shot at 1350 yards or more, there really is a lot of drift. Myself, I’ve been there and beyond a few times but, obviously not enough for 138” deflection to raise a red flag as I came up with it.

    Ok now, in a headwind/tailwind, a 12 degree switch at 10 MPH equals a hell of a lot less deflection than 138”, though still a significant 28”, which is pretty close to equaling the deflection a 2 MPH wind speed change in a 90 degree crosswind would.

    Abinok said >>> 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 reality a 5 degree change is “probably” close to impossible to detect, even with instrumentation, IMHO. I just cant do it, I mean. I would venture to say my ability is probably marginal at best to detect maybe a 15-18 degree switch, probably safer to even say a 25-30 degree, or roughly 5 minutes on the clock face. My basic point here is, this small of change can be very difficult to determine, and even more difficult to feel confident in after you have.

    Although not as contrasting as before, the point should still be fairly easy to see.

    If you look at a 30 degree switch, 12 O’clock to 1 O’clock, and compare the 66 inches of deflection to what would equal 66” of deflection error in a 90 deg. crosswind, you’ll see it is about 5 MPH.

    So in reality, which is easier to detect in order to keep the amount of error to a bare minimum, a 5 MPH wind speed change or a shift from 12 O’clock to 1 O’clock?

    In my experience, a wind speed change from 10 to 5 MPH is easy, way too easy. 1 MPH, not so easy. Detecting a vector shift of less than 30 degrees is quite possible, but it don’t get “much” better than that, “in my experience”.

    In order to make first round hits at real long range like this, or even guarantee your shots are on paper, you must be able to judge wind speed to nearly the exact MPH… this is just the way it is. It’s damn near that bad when you’re getting out near 800-1000 yards... fool yourself not.

    In dead calm wind, I mean dead calm, at “real” long range is hard enough to get first round hits on paper, and you “will” surely see spin drift…. If you account for it and hit paper.

    3 or 4 drinks later, and it's late, hope I didn't make the mistakes here like I made before! /ubbthreads/images/graemlins/wink.gif Thanks for kindly correcting me there too, Abinok... Really. /ubbthreads/images/graemlins/smile.gif
     
  9. abinok

    abinok Writers Guild

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    brent,
    Thanks for posting back! There are a few people that when they post on this board, I pretty much take what they say as gospel, and I think hard and long before I try to correct them. I think I read your post 6 times.....
    Ive been experimenting with a new design of wind flag, based on the "modified daisy" to practice with. Balsa wood is delightfully responsive in light winds. These will track steady in as little as a two mph wind. These have a indicator attached to point to a protractor for a more exact reading, and on the way back from removeing the hold down ropes from my target stand I check every 400 yds or so to get a feel for the wind. I can usually get to 5 degrees resolution if the wind direction is consistant, or find a good average if the wind is switching a small enough angle.
    I definately agree that anything more precise than 15 degrees under hunting conditions, involves a lot of happy thoughts, and crossed fingers. The one oclock/ 12 oclock method is much faster and more practical under hunting conditions.
    I think you definately verbalized the theory that a consistant wind at 90 degrees may be better than a head on wind under most conditions.
    The value I hear most often for match bullet spindrift at 1000 is 2 moa. I was supprised to find only slightly over one at 1350, untill I realized that most people come up from 100 to their 1000 setting. My zero is 500 yds. I think this reduces complications from spindrift substantally.
    Anybody who has experence, or thoughts about determining wind speed and vector beyond 1000, come on in, lets hear your thoughts!