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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
spin drift
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<blockquote data-quote="Shawn Carlock" data-source="post: 191044" data-attributes="member: 4"><p>While it might be possible to build a program to determine spin drift for a given combo, I think it would be nearly impossible to run all the possible combos available. While testing the 300 WM 190 gr there was a noticable difference in a 10 twist barrel vs a 9 twist. Also there was a subtle but consistance difference between 2 1-10 twist barrels of different rifling profiles. I believe that spin drift is an important factor at distance but truly requires some testing and practice to deal with. Once again even if we had a program to determine SD it would still be just a place to start field testing. Once you have the effective wind speed figured out to equate the SD, it has proven to be an accurate method of prediction in the testing I did from 1800-6600ft, 35-80 degrees, 30-80% humidity in various combinations and distances out to just over 1500 yards. In the Nightforce ballistics program I simply entered .85 mph right wind into the base chart and saved it. If I had an estimated wind of 6mph left, I entered 5.15 mph left. This provided for some truly outstanding first round hits on rocks of the 10-12" range at 1500+ yards. Without the SD compensation the would have mostly been close misses written off to slight wind estimation errors. It can drive you nuts but I really dig this stuff.</p></blockquote><p></p>
[QUOTE="Shawn Carlock, post: 191044, member: 4"] While it might be possible to build a program to determine spin drift for a given combo, I think it would be nearly impossible to run all the possible combos available. While testing the 300 WM 190 gr there was a noticable difference in a 10 twist barrel vs a 9 twist. Also there was a subtle but consistance difference between 2 1-10 twist barrels of different rifling profiles. I believe that spin drift is an important factor at distance but truly requires some testing and practice to deal with. Once again even if we had a program to determine SD it would still be just a place to start field testing. Once you have the effective wind speed figured out to equate the SD, it has proven to be an accurate method of prediction in the testing I did from 1800-6600ft, 35-80 degrees, 30-80% humidity in various combinations and distances out to just over 1500 yards. In the Nightforce ballistics program I simply entered .85 mph right wind into the base chart and saved it. If I had an estimated wind of 6mph left, I entered 5.15 mph left. This provided for some truly outstanding first round hits on rocks of the 10-12" range at 1500+ yards. Without the SD compensation the would have mostly been close misses written off to slight wind estimation errors. It can drive you nuts but I really dig this stuff. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
spin drift
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