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Updraft question ?

 
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  #15  
Old 09-15-2008, 08:21 PM
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Re: Updraft question ?

AJ,
Thanks for confirming my #'s. Glad to see I was on the right tract. Being a " flatlander " here in the midwest, I don't get an opportunity to take a shot like this in practice.
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  #16  
Old 09-15-2008, 08:24 PM
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Re: Updraft question ?

Quote:
Originally Posted by trueblue View Post
AJ,
Thanks for confirming my #'s. Glad to see I was on the right tract. Being a " flatlander " here in the midwest, I don't get an opportunity to take a shot like this in practice.

I got -0.07 MOA, not .7

AJ
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  #17  
Old 09-15-2008, 08:40 PM
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Re: Updraft question ?

Thanks AJ, I uhhhhhhh...didn't know that my shiny new toy had that feature change.
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  #18  
Old 09-15-2008, 08:41 PM
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Re: Updraft question ?

Quote:
Originally Posted by Bravo 4 View Post
I got the .25moa less drop from 742 yards compared to the 750 yards. That was from both exbal and JBM. I did account for the down draft on the opposite side, but about as much as I accounted for the up draft on the shooter's side...none.
My daughter and I drew an illustration of the scenario if anybody wants me to send it to them and they can post it. I'm not smart enough, as the drawing will prove!!!

Here is your picture. (yes you sent me the right one, ;))

AJ

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  #19  
Old 09-15-2008, 08:42 PM
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Re: Updraft question ?

So,
Can someone show me the math so I can see where I went wrong.
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  #20  
Old 09-15-2008, 09:55 PM
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Re: Updraft question ?

I have worked quite a bit with this kind of shooting problem in canyon shooting. I would have done this:
1. Ran my PPC for 750 yards @ .99 cosine and got my dope.
2. Noted the head wind velocity and the apparent angle of the facing slope being 20 degrees or so and around 4-5 mph.
3. I would consult my wind reading for 4-5 mph at 500 yards as this is 2/3 of the shot distance. This would be about 1.00 moa, now 20 degrees is roughly 1/4 value in wind making the effective updraft about 1/4 moa on paper. I have found the wind to almost always be faster in the open air than by the walls so I would have backed off .50 moa from the computer generated dope for 750 @.99. If you have my video the 1602 yard shot is suffering from the same effect but from a different direction. On that shot we used the method I just outlined and backed 2.00 moa off and were still .5 high on the first shot. It maybe hard to put to paper but I have seen this effect to cause repeated high bullet strikes in a varity of conditions. It takes a bit of practice because I have not seen the down draft from the opposite canyon wall have much if any effect. I have seen many times the down draft from a tailwind in this same scenerio cause a drop in bullet impact and require more elevation. I figure the correction the same way only add the offset. This is how I have done it, but as with anything wind related it is always your best guess.
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  #21  
Old 09-17-2008, 12:30 AM
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Re: Updraft question ?

Thanks all for the detailed responses. I think you guys are all on the same page. Speaking the same language !

I see where you are coming from and understand the math now .

Many thanks guys !!

Cheers for now

DUH
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