Need Help with Wind Chart...

[RonAKA]

Hopefully this is not a "what's the best way to clean your barrel" question. Some time ago in a .22LR rimfire forum a wind chart was posted that was said to illustrate the effect of wind from the 12 clock positions. See below:

The general gist is that a side wind from the right deflects the bullet not only left, but up. And a wind from the left deflects the bullet right and down. Also head winds deflect down, and tail winds lift. That all seems to make some sense, and at first I thought the chart reflected that.

However, when you look at the chart closer, there is a relative huge step change in point of impact when you go from 6 o'clock to 7, and also from 12 to 1. Seems to me there should not be an any larger step change there compared to any other one position change?

Comments? Better chart out there? My frame of reference is .22LR at 50 meters, and 6BR at 100-300 meters.

 

[gunsandgunsmithing]

I agree with the chart and try not to shoot in a switchy head or tail wind because of it. The majority of the vertical component reverses between 6 and 7 o'clock, as well as 5 to 6 and 11 or 1 in relation to 12. Is that clear as mud now or what? ???--Mike Ezell

 

[madmixerman]

This may be a dumb question but where would you aim your crosshairs (dot) to make the bullet hit dead center if the wind was blowing from the 10 o'clock position?

 

[brxbrad]

Check out this link on wind vector and bullet impact chart
Maybe it will help...
http://tmtpages.com/WindVector.htm

 

[RonAKA]

This may be a dumb question but where would you aim your crosshairs (dot) to make the bullet hit dead center if the wind was blowing from the 10 o'clock position?

If I read the chart correctly, you would have to aim at the green 4 circle near 10:00 o'clock.

 

[RonAKA]

Check out this link on wind vector and bullet impact chart
Maybe it will help...
http://tmtpages.com/WindVector.htm

Thanks Brad. The text sounds good, but for some reason the graphics will not display in that link.

 

[ronsroom1]

http://www.uslink.com/~tom1/windvector.htm

Try this link for printable wind charts.

I clicked on FILE in my toolbar, then print, and got all 3.

Will do it on my wifes color printer later.

The medium size one fits in the inside cover of my MTM-Case Guard 100 rd. center tray .22 box.

 

[RonAKA]

http://www.uslink.com/~tom1/windvector.htm
Try this link for printable wind charts. I clicked on FILE in my toolbar, then print, and got all 3. Will do it on my wifes color printer later. The medium size one fits in the inside cover of my MTM-Case Guard 100 rd. center tray .22 box.

Ronsroom1, thanks for the link. I can see this one. However, it appears to be essentially the same one as I originally posted. I have a problem with the 1, 2 and 7, 8 points. They don't make sense to me, but I'm still thinking on it...

 

[RonAKA]

I was loaned a book called Rifle Accuracy Facts, authored by Harold Vaughn. I believe he is retired now, but was a specialist in aeroballistics. It is a very interesting book and he has exactly answered my question, and I now believe based on the data he presented in the book that the initial wind rosette that I posted is not correct. The main reason is that a straight 12:00 or 6:00 wind has no significant impact on vertical POI. He calculated the effect to be 0.007" at 100 yards. The side wind vector is very significant because it cases the bullet to nose into the wind and drift. A 6BR at 100 will drift about 1" from a 3:00 and 9:00 wind. Surprisingly the angle where it is significant is quite wide. At the 30 degree off pure left and right (2,4,8, 10:00) you still get 87% of the full drift, and 50% at 60 degrees off (1,...)

The gyroscopic lift and drop is significant. At 100 yards you get about 1/3 as much lift and drop as pure left right drift. The amount of lift and drop is dependent on the stability factor of the bullet. This is for a factor of 1.5. If the bullet is being overspun with a fast twist barrel, then the lift and drop increases. The gyroscopic movement is linear with range, double the range double the lift and drop. This is different than drift where the drift is 4 times if you double the range. So the gyro effect becomes less significant compared to the pure drift as you go out further.

I made a crude attempt to fix up the wind rosette I posted based on this data from Vaughn. Essentially the wind and gyroscopic effect move the bullet left and up at 17 deg. from the 3:00 wind, and the same to the right but down from a 9:00 wind. I left off some of the clock positions as they would be right over top of other ones. For example the 5:00 is the same as the 1:00 and 4:00 is the same as 2:00.

What this seems to suggest is that a wind shifting from 11:00 to 1:00 and the same with a similar tail wind, would be very nasty to deal with. It is much better to have it shifting from 2:00 to 4:00.

If anyone has any questions on the Vaughn data ask quick while I still have the book!

 

[tunered]

This chart was made up for 22rimfire, not centerfire, whole different game. [ First chart posted]. ed

 

[RonAKA]

This chart was made up for 22rimfire, not centerfire, whole different game. [ First chart posted]. ed

Agree it probably was. However if you scale back a rimfire to 50 yards, the result is probably not that different. Wind drift for 10 mph at 50 is about 1" for a target style subsonic bullet. Time to the target is going to be about 50% longer, so rise or drop caused by a tail or head wind, is not likely to be more than 50% or double that of a centerfire at 100. I'm thinking 0.014" at 50 yards for rimfire is close to insignificant as well, and certainly would not show on a graph showing 1" lateral drift.

 

[333smitty]

IMHO, In regards to competition shooting. I don't care what the chart says always go to your sighter first and confirm POI and and then make your aimpoint ajustments. Hvy or light winds can and will make the chart useless.

 

[artbosco]

IMHO, In regards to competition shooting. I don't care what the chart says always go to your sighter first and confirm POI and and then make your aimpoint ajustments. Hvy or light winds can and will make the chart useless.

I strongly agree with smitty, I've never had a bullet follow a wind chart. They just can't read them, and neither can the wind. Watch your target for clues as to what they intend to do on any particular day. Substitute Wind Flags for a chart.

 

[necchi]

Another one that agrees with the 2 above and,,
,,+1 on the flags.
The charts are good for a person to actually get an idea that more than one thing is going on with a cross wind.
I've seen as a shooter and a Range Officer at comps the flags going different directions in as short as 100yrds, so the bullet usually isn't getting hit with a wonderfully direct and steady wind. Even if it was, if you put a 2' rise in the ground 200yrds UP wind on an otherwise flat playing field, funny stuff happens

 

[artbosco]

I've seen as a shooter and a Range Officer at comps the flags going different directions in as short as 100yrds, so the bullet usually isn't getting hit with a wonderfully direct and steady wind. Even if it was, if you put a 2' rise in the ground 200yrds UP wind on an otherwise flat playing field, funny stuff happens

The the new Rick Graham “uppy/downy” vertical indicating wind flag is a great tool for pinpointing when that "funny stuff happens." Go the the bottom of this link to see what I'm talking about: http://www.brflags.com/flags.html

I've seen four and five flags, spaced out over 100 yards, each going in a different direction, many times. You should see what happens with six flags spaced out over 200 yards. It's amazing what's going on out there, and flags, are one of the things that are going to reveal it to you. Unlike trees, grass, bushes etc. you can place the flags where you want them.