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wildcard
04-21-2008, 6:50 PM
So I had the chance to go do some shooting at Burro Canyon today and experienced something new that I can't quite figure out.

Facts:
I was shooting at a 500 yd target along a ridge. The mountainside is on the left hand side and the mountain drops off to the right. The wind was blowing from right to left at 15 MPH.

I dialed in my usual elevation and wind but I was hitting 7 inches high! Afterwards I dialed it down 1.5 MOA and hit it fine. Then when the wind died down, I ended up hitting 7 inches low. I was sure confused because it has never happened before. If it makes any difference, this was about 3 PM, sunny, 75 degrees. And yes, my original dope has been fine many times before at this location even with wind.. of course it was colder before which may not have affected the wind flow like today.

Anyone have an answer? My guess is that the wind was not only blowing right to left.. but also from the bottom right to the top left up the mountainside..

Cypriss32
04-21-2008, 7:17 PM
Watch Shooter it will tell you everything!

aplinker
04-21-2008, 7:46 PM
Colder air has more resistance. If it's warmer that will make it different.

So I had the chance to go do some shooting at Burro Canyon today and experienced something new that I can't quite figure out.

Facts:
I was shooting at a 500 yd target along a ridge. The mountainside is on the left hand side and the mountain drops off to the right. The wind was blowing from right to left at 15 MPH.

I dialed in my usual elevation and wind but I was hitting 7 inches high! Afterwards I dialed it down 1.5 MOA and hit it fine. Then when the wind died down, I ended up hitting 7 inches low. I was sure confused because it has never happened before. If it makes any difference, this was about 3 PM, sunny, 75 degrees. And yes, my original dope has been fine many times before at this location even with wind.. of course it was colder before which may not have affected the wind flow like today.

Anyone have an answer? My guess is that the wind was not only blowing right to left.. but also from the bottom right to the top left up the mountainside..

Mute
04-21-2008, 7:54 PM
How close was your shooting spot to the place where the land rises up the slope? Based on your description, the strong wind coming towards the upslope and your close proximity to the upslope might be enough to have some lift effect on the bullet.

Timberwolf
04-21-2008, 7:55 PM
Never been there but it sounds like a canyon thermal

Fjold
04-21-2008, 7:58 PM
Here's a theory:

Gyroscopic precession, when force is applied to a spinning object the direction of travel is 90 degrees to the force applied.

It is something to take into account when shooting at very long range.

I shot a high power match in Lima Ohio a long time ago. We had a strong 20+ mph wind coming right into our faces. My first sighter hit almost a foot high and that baffled the crap out of me. I watched the shooters (locals) adjusting their sights down so I just sat there watching them. After awhile I figured out that the incoming wind was hitting the back side of the berm (in front of the pits) and going straight up in front of the target.

wildcard
04-21-2008, 8:18 PM
Colder air has more resistance. If it's warmer that will make it different.

I wish the answer was that simple :)

Cypriss32
04-21-2008, 8:19 PM
I gave you the answer just watch it! It goes into great detail!

wildcard
04-21-2008, 8:20 PM
How close was your shooting spot to the place where the land rises up the slope? Based on your description, the strong wind coming towards the upslope and your close proximity to the upslope might be enough to have some lift effect on the bullet.

I was shooting off one ledge... and then the bullet travel along another ledge.. maybe 50 yds from the drop off..

rksimple
04-21-2008, 8:30 PM
1.5 MOA sounds a bit excessive for it to be all updraft. Was there an isolated low pressure system hovering over burro???:D

Did you get any dope at other distances?

wildcard
04-21-2008, 8:31 PM
Never been there but it sounds like a canyon thermal

That's what i'm thinking.. never experienced it except when at APS though. Where in the world was it all the other times I shot? I guess. there's a upward thermal in the summer WITH wind.. but no downward thermal..

wildcard
04-21-2008, 8:53 PM
1.5 MOA sounds a bit excessive for it to be all updraft. Was there an isolated low pressure system hovering over burro???:D

Did you get any dope at other distances?

100 - 400 yds was just fine.

Cypriss32
04-21-2008, 9:04 PM
Were you shooting noslers?

wildcard
04-21-2008, 9:08 PM
Were you shooting noslers?

Nope.. only 168 SMK for me.

Cypriss32
04-21-2008, 9:12 PM
****ing Noslers........


Anyone want to shoot Friday? Gona take out the new new wsm and HK expert!
http://i6.photobucket.com/albums/y230/adam5432002/WSM.jpg

PUFF
04-21-2008, 9:19 PM
Fjold is half correct. the updraft and air density build up against the slope help lift your impact.[Like skipping a rock on water]Much more happens than that but it would take a long explanation. The other part that happens is that air is like water in that it bends light. Fjold I'm sure you remember the rule to never shoot in a boil.[Similar situation with the air rising up the slope] When the mirage is boiling, it makes your target appear higher or lower because it is bending the light coming at you. I have seen many new FClass shooters shoot a high 8. Then make an adjustment to shoot a low 8 during a boil.

Pascal
04-22-2008, 7:07 AM
From my experience it's not just thermal

I did some long distance shooting in the Arizona desert shooting from one hill to another, and during the monsoon, we would have strong winds moving between the hills and UP the hills as well. UP the hill where the target was and UP the hill where I was located. That's 2 UP wind.

I remember some 650 yards shooting from the top of one hill to the slope of another one and in the last 100 yards where the target was, there was a 10-15 MPH wind going up. Where I was located, I had a strong 10 MPH wind moving UP the hill in front of me (which I kind of assumed to be in the first 100 yards like the other hill). In between, the wind was going 15 MPH to the East.

So I used 7 MPH wind to my elevation (to eliminate the fact that there was no up wind in between) and 15 MPH windage for the East wind.

It can screw with your mind :)

It's like a reverse windage. Instead of using the windage knob, you have to use your elevation knob and add the wind into it.

Good training on wind call though!

Oh...I did hit the target :cool: I was still a bit low but it was a hit.