Effect of Wind

[Hanic]

Greetings all,

I went to the range last W/E with the latest refinement to my 6mmBR load with the goal of shooting a 1" group at 400yds. After fouling the barrel and just settling in for about 10 shots, I started to seriously try for my goal with four 3 shot groups. Three of the groups ranged from 1 to 1 5/8", the 4th one was ruined by a flinch. Then I got real serious and started shooting 5 shot groups. They varied from 2 3/8 to 4 5/8". I noticed the wind was picking up. The wind was basically blowing up range all day, swinging the 2 foot long surveyors tape tail on my home made wind vane from about 30 deg left of straight down range to about 30 deg right. I tried waiting for calmer periods during the last 2 groups with no real improvement in group size.

So my question is - will the observed wind, 30 degrees left and right of center, blowing a 2' piece of surveyors tape about 60 degrees up from vertical, increase my group size from 1.5 " to 3 "? The load was 6mmBR with the Horn 87gr VMax. Please tell me how sure you are of your advise.

Thanks in advance for any input. Hanic

 

[benjamin199]

Yes it can.
I shoot the Berger 95 VLD at 2940 for my match load.
If I plug a 5 mph wind from 7 O'clock into my ballistic program it gives me about 2.5" of drift at 400 yards, a 5mph wind from 5 o'clock would give 2.5" of drift in the other direction. So a fishtailing tail wind can most definitely open your groups up from 1.5 to 3" and do more if you don't compensate for it.

 

[jb1000br]

key info needed...what was the shape of the group? horizontal and vertical dims?

JB

 

[Hanic]

Thanks Ben,

That's the kind of response I was hoping for and dreading. The load is up to the task, but my wind reading skill is way under par. But, I can work on that. Thanks



To jb1000

A great question. The 4 groups measured 3.25 W by 1.25 H; 4.5 by 3.5; 2.25 by 2 and 3 by 0.875. This suggests that the load is up to snuff and the rifleman has some vertical spread issues.

Thanks for the great responses, I'm happy to realize that I'm close to the goal,5 shots into 1", more than once). Any other feedback is welcome. Hanic

 

[rayjay]

Depending on the physical elements of your shooting range you can get all kinds of vertical with certain winds. The baffles and roof covering the benches at my range are basically the shape of an aircraft wing with the flaps down. A wind at the shooters back gives a big downward push to the bullet.Normally you would expect a tail wind to raise the bullet poi but not at this range.

At our last match I had a big condition change after the first shot. I waited until there was only about 90 seconds left and I still had the wind at my back. I went down and got a couple of sighters to see the new poi which was about a third of the mothball low and right. I went up the the record target and held off that amount and fired a shot very close to the first one. I then blazed away the last 3 for a .5 at 200 which was my best group at that yardage. The last shot was fired off after the 15 second warning:wow:

I also had 2 or 3 200 yd targets that had 4 shots touching in app .3 but always the 5th hole was out making the group a .7 or .8 :, Others were doing worse and I got 4th at 200.




I would like to set off a few smoke bombs one day to watch all the swirling.

 

[M700]

Wind.. Yup, it's a booger! When I figure it out, I'll let ya know!

 

[Hanic]

To benjamin199

My next gun would be either a 6.5 by 47L or the 6mm version. the 6.5 would drive a 50% heavier bullet at about the same speed, while the 6mm version would drive the same bullet about 400 fps faster. Assuming the same BC, which setup would have the better wind resistance. I'm guessing the heavier bullet, but I'd like to know what your ballistics program predicts, if you have the time to run the question. Thanks, Hanic

 

[benjamin199]

If both bullets have the same BC, the faster bullet should have less drift. The thought that heavier bullets have less drift comes generally from heavier bullets usually have a higher BC than lighter bullets for the same caliber.

 

[SlowpokeRodriguez]

I do not agree about wind being bad in competition---separates the men from the boys. In the field its is a bugger but with practice it can become manageable..

 

[treeman]

the wind is your friend and mirage is user friendly

 

[SlowpokeRodriguez]

True statement about mirage it can be your friend just like the wind!!!

Something to contemplate when looking through a scope or a telescope, "the mirage appears to move with the same velocity as the wind, except when blowing straight into or away from the scope. Then, the mirage gives the appearance of moving straight upward with no lateral movement. This is called a boiling mirage. A boiling mirage may also be seen when the wind is constantly changing direction. For example, a full-value wind blowing from 9 o’clock to 3 o’clock suddenly changes direction. The mirage will appear to stop moving from left to right and present a boiling appearance. When this occurs, the inexperienced observer directs the shooter to fire with the "0" wind. As the shooter fires, the wind begins blowing from 3 o’clock to 9 o’clock, causing the bullet to miss the target therefore, firing in a “boil” can hamper shot placement. Unless there is a no-value wind, the shooter must wait until the boil disappears. In general, changes in the velocity of the wind, up to about 12 miles per hour, can be readily determined by observing the mirage. Beyond that speed, the movement of the mirage is too fast for detection of minor changes.