Compensating for spin drift...

My thoughts: You're going to have to be a darned good shot with an exceptional rifle shooting in a dead calm (or a tunnel) to notice that "spin drift".
 
Bart B. said:
I don't know of any top classified NRA long range rifle shooter who ever gets concerned about spin drift.
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fileofile is talking about those who shoot at targets that are at unknown distances (sometimes with only one chance) and didn't have the opportunity to sight their rifles in 'half an hour earlier'.

Therefore, it's to this other shooter's advantage that any variables that can be reduced or mitigated, are.
 
SOTIC it was taught the basic rule was one click (1/2 moa) for any shot over 600 meters.

That is making head shots at 1000 meters with 7.62mm match.
 
davidsog,

There was another click at 800m for a full MOA.

Ah, the good old days of getting by with a wind knob that was 1/2 MOA per click and a BDC that was 1 MOA per click.
 
I do not remember another click at only 200 meters past the initial 600. That maybe something later that was taught later or earlier.

I can look it up in the manual when I get home.
 
Spin drift is:

3-131. The lands and grooves in the bore of the rifle impart a rotational motion to the bullet about its own axis. This rotational motion causes the projectile (as it travels through the air) to shift in the direction of rotation (in almost all cases to the right). This motion causes a drift that is caused by air resistance. A spinning projectile behaves precisely like a gyroscope. Pressure applied to the front of the projectile (air resistance) retards its forward motion but does not significantly upset its stability. However, upward pressure applied to the underside of the projectile (due to its downward travel caused by gravity) causes it to drift in the direction of spin. This drift is relatively insignificant at all but the greatest ranges (more than 1,000 yards).
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So the 1/2 MOA correction for spin drift at ranges 600 meters or greater on a M118 7.62mm works great in both theory and practical application.
 
So the 1/2 MOA correction for spin drift at ranges 600 meters or greater on a M118 7.62mm works great in both theory and practical application.
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Not in my experience. At 600 meters the effect of spin drift is negligible. To back to the chart uncle nick posted. I believe it shows drift at 600 yards being roughly 1/2 minute give or take a tenth. At 600 yards, a half minute is a shooters 3 inches. If you consistently have to hit within closer than 3 inches at that distance, as Bart B says you have far greater concerns.

OP, unless you have experience shooting out last 600 yards and plan to continue to do it frequently, I would not worry about spin drift. Get your rifle, hit the range, and learn to make good wind calls. Good wind calls are the bread and butter of long range shooting. Any trained monkey can work out holdover on a known distance range (estimating range without a LRF at a U/K distance range is a different matter), but reading the wind over distance, when it changes speed and direction several times between you and the target, is quite the feat to master. I agree with Bart B entirely on this matter. Debating spin drift is not for novice shooters.
 
I shoot 600 yds weekly at my gun club and typically I dial about .5 moa and this seems a reliable SD compensation. However if its a windy day I may just leave this alone. When I shot the Sig 1000 yd instructional class my calculated SD was about 7" . It was a real eye opener as to how much more critical your calculations affect poi at 1000 yds vs 600 yds.
 
If you consistently have to hit within closer than 3 inches at that distance, as Bart B says you have far greater concerns.
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Well think about it. :p

SOTIC

Special Operations Target Interdiction Course....
 
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