"If" spin drift exists, then it is repeatable and in one direction. In this case, you CAN count on it and account for it, independ of your wind reading ability.
Linda Miller and Keith Cunningham, in their book "The Wind Book for Rifle Shooters", say that the effect of spin drift is largely unnoticeable at shorter ranges, but equates to about 1 MOA at 1000 yards for .308. They even go so far as to mention that "serious" competitors often use a separate rear sight dedicated to a given long range and zeroed windage-wise to compensate for spin drift at that range. I assume they would know what they are talking about, and would have no reason to lie.
Service rifle match shooters wouldn't normally notice whether there is a spin drift effect or not, so I'd be more inclined to listen to the Long Range (1000 yard) and Palma (800, 900, 1000 yards) competetive shooters. One poster said it perfectly when he said there's ALWAYS wind past 500 yards, and those that choose not to accept spin drift will just attribute it to wind. Fine. Shoot your sighters and adjust from your last shot and you'll have no reason to recognize or worry about spin drift, even at 1000 yards; it's just "wind" at that range. Who's to prove it isn't. How can one possibly? But, when 1000 yard competetive shooters see a trend after long experience, then it might be time to listen, IMO.
And, as has been said, a rifle with a right-hand twist barrel is still a right-hand twist rifle when up-side-down. So, a no-go on that.
But, to the op, 1 MOA at 600 yards isn't all spin drift. Most of that 1 MOA must be something else, so I would check for canting first and foremost.
Linda Miller and Keith Cunningham, in their book "The Wind Book for Rifle Shooters", say that the effect of spin drift is largely unnoticeable at shorter ranges, but equates to about 1 MOA at 1000 yards for .308. They even go so far as to mention that "serious" competitors often use a separate rear sight dedicated to a given long range and zeroed windage-wise to compensate for spin drift at that range. I assume they would know what they are talking about, and would have no reason to lie.
Service rifle match shooters wouldn't normally notice whether there is a spin drift effect or not, so I'd be more inclined to listen to the Long Range (1000 yard) and Palma (800, 900, 1000 yards) competetive shooters. One poster said it perfectly when he said there's ALWAYS wind past 500 yards, and those that choose not to accept spin drift will just attribute it to wind. Fine. Shoot your sighters and adjust from your last shot and you'll have no reason to recognize or worry about spin drift, even at 1000 yards; it's just "wind" at that range. Who's to prove it isn't. How can one possibly? But, when 1000 yard competetive shooters see a trend after long experience, then it might be time to listen, IMO.
And, as has been said, a rifle with a right-hand twist barrel is still a right-hand twist rifle when up-side-down. So, a no-go on that.
But, to the op, 1 MOA at 600 yards isn't all spin drift. Most of that 1 MOA must be something else, so I would check for canting first and foremost.
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