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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: 190947" data-attributes="member: 4"><p>I recently did a bunch of testing with diffferent calibers at distance to determine the effects of spindrift at the request of Nightforce scopes. I mostly confirmed what I already knew about spin drift.</p><p>1. Spin drift exists in all calibers, some so slight as to not be practically detectable, others quite a bit.</p><p>2. Spin drift will be effected differently in the same caliber by velocity, twist rate, bullet profile and atmo conditions.</p><p>3. Spin drift is predictable after some testing, after determining the spin drift (this is not real easy) at a given distance like 1000 yards other distances can be predicted by entering it as a wind function. After determining 1000 yard drift I was able to predict 1500 + drift using the wind drift function and my 1000 yards info as a validation number. It will be a small number usually less than 1 mph of wind. </p><p>4. The longer and higher BC a bullet the more suseptable it is to spin drift.</p><p>5. Proper twist rates reduce spin drift but don't eliminate it.</p><p>6. If spin drift is roughly 1 mph or less in most calibers few can estimate the wind that accurately. This doesnt mean that you should discount spin drift as it is, at distance one of the small compounding errors that can make a miss. I believe that these misses are more often interprited as wind estimate errors.</p><p>7. Every single change in platform can effect spin drift differently, velocity, twist etc.</p></blockquote><p></p>
[QUOTE="Shawn Carlock, post: 190947, member: 4"] I recently did a bunch of testing with diffferent calibers at distance to determine the effects of spindrift at the request of Nightforce scopes. I mostly confirmed what I already knew about spin drift. 1. Spin drift exists in all calibers, some so slight as to not be practically detectable, others quite a bit. 2. Spin drift will be effected differently in the same caliber by velocity, twist rate, bullet profile and atmo conditions. 3. Spin drift is predictable after some testing, after determining the spin drift (this is not real easy) at a given distance like 1000 yards other distances can be predicted by entering it as a wind function. After determining 1000 yard drift I was able to predict 1500 + drift using the wind drift function and my 1000 yards info as a validation number. It will be a small number usually less than 1 mph of wind. 4. The longer and higher BC a bullet the more suseptable it is to spin drift. 5. Proper twist rates reduce spin drift but don't eliminate it. 6. If spin drift is roughly 1 mph or less in most calibers few can estimate the wind that accurately. This doesnt mean that you should discount spin drift as it is, at distance one of the small compounding errors that can make a miss. I believe that these misses are more often interprited as wind estimate errors. 7. Every single change in platform can effect spin drift differently, velocity, twist etc. [/QUOTE]
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