Updraft question ?
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AJ Peacock
Well-Known Member
AJ Peacock
Well-Known Member
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
Shawn Carlock
Sponsor
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.
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.
Down Under Hunter
Well-Known Member
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
I see where you are coming from and understand the math now .
Many thanks guys !!
Cheers for now
DUH
Down Under Hunter
Well-Known Member
Here is your picture. (yes you sent me the right one,
AJ
AJ,
Cheers mate for going to the trouble with the ppic. That is exactly what I had in mind.
Much appreciated my friend !
DUH
AJ Peacock
Well-Known Member
Yeah DUH, Bravo4's daughter drew it, I just posted it. Credit where credit is due
AJ
