I had 2.25 MOA dialed in for windage, the correction my B7 gave for 5mph at 1312 yards. Do you think that was too much?
Jack, my 338 LM with a 300 OTM, MV of 2800 shooting at roughly 4000 ft altitude is ike this.
5 mph full value wind at 9:00 or a left wind. the correction would be .8 moa left for spin drift and adding 5 mph left wind a total of 3.5 moa left correction.
The same shot with a 5 mph right wind from 3:00 would be a total correction of 2 moa left.
It gets a little confusing adding or subtracting spin drift . But your right twist barrel will have a SD correction of over 10" left at 1300 yards.
Thanks for your time. I think I understand the SD effect now that I read a bit on it, I had not considered it before.
So, if I have a 9 o'clock 5 mph wind I should add .8 MOA to the correction for the windage the B7 gives no matter the distance -and subtract .8 MOA for a 3 o'clock wind?
So, if I have a 9 o'clock 5 mph wind I should add .8 MOA to the correction for the windage the B7 gives no matter the distance -and subtract .8 MOA for a 3 o'clock wind?
And would the correction double in a 10 mph wind?
Thanks again,
Jack
No SD is relevant to distance. That .8 was for a 1300 yards shot with your rifle. It would only be .5 moa at 1000 yds
Since your rifle has a right twist barrel you will have right spin drift. So the correction for the SD will always be a left correction and is completely seperate from wind drift.
My ballistic calculator has the option to always correct for SD and I leave it on all the time. So it always adds or subracts it from my shooting solution it gives me when I enter all field conditions and distance.
As soon as I can get set up for reloading and can stop shooting these tightly wrapped $5 dollar bills I need to shoot enough to develop a correction chart for shots beyond a 1,000.
For now I'll use a politically correct adjustment;
Be liberal when adjusting for winds from the left
Be conservative when adjusting for winds from the right...
I've been using that G7 rangefinder this year. With careful fine tuning I have found no need to develop a chart for shots over 1000 yards. Mine was giving me dead accurate ballistic solutions out to 1380 yards last weekend. What I failed to add was the extra click in windage for spin drift at that range. I have my LR scopes zeroed .5 MOA left and that compensates nicely for spin drift out to 1K.
That shifty 5 mph wind at 1300 is real challenging, especially if it switches directions as well. I shoot marmots a lot in above-timberline basins. The winds are usually pretty shifty when they pick up. Last weekend they were not only gusting 0-5, but shifting frequently in direction. I am still learning to read the wind, so I was hitting a half MOA on one side, then again to the other side. Very frustrating. I squeezed one off during a momentary lull and hit the edge of a tennis ball sized target. It was a good one to quit on, so I packed up and went home.
No SD is relevant to distance. That .8 was for a 1300 yards shot with your rifle. It would only be .5 moa at 1000 yds
Since your rifle has a right twist barrel you will have right spin drift. So the correction for the SD will always be a left correction and is completely seperate from wind drift.
My ballistic calculator has the option to always correct for SD and I leave it on all the time. So it always adds or subracts it from my shooting solution it gives me when I enter all field conditions and distance.
Jeff
Jeff i couldnt agree more on spin drift. I was shooting yesterday with some buddys that is going with me to Co, this year. They shot at 500 than 800 and stopped with there euiptment. I broke out my edge at 1220 yards. My first shot at a jug was high due to i used drop chart for 1400' and was shooting at 2550'. I dialed down 3/4 moa elevation fine. I left othere shoot and they held 2 moa for wind and was still off around a 4-5 mph wind. I got up and held almost 3 moa and hit the jug. I told them rhand twist its going right have to allow for that besides the wind. I have never seen spin drift discussed to much but i have sure learned what it can do.
MIke
Jack, my 338 LM with a 300 OTM, MV of 2800 shooting at roughly 4000 ft altitude is ike this.
5 mph full value wind at 9:00 or a left wind. the correction would be .8 moa left for spin drift and adding 5 mph left wind a total of 3.5 moa left correction.
The same shot with a 5 mph right wind from 3:00 would be a total correction of 2 moa left.
It gets a little confusing adding or subtracting spin drift . But your right twist barrel will have a SD correction of over 10" left at 1300 yards.
Jeff
Jeff, where can I go get my spin drift data for my 338WM (24 3/8" 1/10"R) 185gr GMX, MV 3,009 @ 9,928'....in the snow-no wind {:>)? Don't do moa's Zeiss Victory Diavari 4-16x50 T* FL 30mm and run their in house Reticle analysis to get "Optimum Power so my Rapid Z 800 will be right on for drop chart for temp - alt. and MV changes. What would be my "SD correction of over X" left at 800, 900 & 1,001 yards"? Please forgive the underrange-some times you have to go where the preacher is.
__________________ "I'm better when it's breathing" Chris Kyle NRA Life Member 1970