Home Forums Hunting & Shooting Ask The Gunwriters Spin Drift and a Zero?

Cause wind has much more effect on impact than spin drift. And if your zeroed at 5 on some windless day?? you have any spin drift compensated for with the zero.
Now you still have to call the wind, when it appears...which it will.
If you watch the mirage move through a spotting scope, even at 200 yrds with a mild 5-7 mph wind, full value or other wise, you`ll forget about spin drift.

Fun and interesting to talk about, but IME, application gets lost in the wind....or is it "Gone with the Wind"?

YMMV

Thanks for that last nugget. DIdn't know that.

After 49 years of big game hunting, and guiding well over 150 hunters in the past, it's my opinion that the vast majority of hunters, especially those that aspire to excel at extended ranges, don't shoot well enough to know whether it's spin drift, wind, shooter error, bad ammo, poor form, scope issues, mount issues, etc. I've killed well over 300 head of big game and didn't even spin drift existed until reading about it a year or so ago. Therefore in my world it's a big non issue.

Egad man, how did you ever do it?

And without a Creedmore, who thought this possible?

This^^^^^

Here are results from the ballistics program for my 6 Creed at 500 yards. Spin drift is 1.13 inches at 500 yds. Adding only a 1 mph crosswind completely offsets the spin drift. I spend quite a bit of time shooting at long range steel and I can say with certainty I can’t read a 1 mph wind in hunting conditions.

The choice of bullet matters. Spin drift is a relatively small effect, but the ratio of spin drift vs. wind drift gets higher when the BC of your bullet increases, possibly to the point of no longer being lost in the noise.

SWAG'ing it I guess !

That`s interesting. Any numbers suggesting when that could happen?

Welcome to the "Fire" White Feather!

It's really only likely in the case of very little wind. Spin drift is proportional to SG and also to TOF^1.83, and wind drift is proportional to (TOF - TOF_vacuum), so in the case where bullet BC, bullet length, and muzzle velocity maximize SG and TOF, while minimizing (TOF - TOF_vacuum), spin drift becomes most significant compared to wind drift.

As an example of when spin drift can matter, consider the 120 gr 7mm VM leaving the barrel at 2975 fps. In SAC, an 8" RH twist results in 20.4" of spin drift at 1000 meters. Each 1 mph of wind is responsible for 16.3" of wind drift, so with a 9 o'clock 1 mph wind the total drift is 36.7" to the right. But if instead you have a 3 o'clock 1 mph wind, your total drift is 4.2". So if you were to mistakenly assume a 0 mph wind, and if you don't account for spin drift, you could be off by nearly 3 feet of drift to the right. It's an issue similar to tolerance stacking, where if unaccounted for the small errors can stack up to create a large error.

Well dang, might as well throw in Coriolis effect while your at it.

JMHO-
I make my judgment for my own hunting rifles
with 1 shot from a cold barrel. That's the only
one that counts for my purposes.

Well, you got me thinking. Shooting the 308 in HP at 600 and Palma matches,8,9, and 1k, wind was always a factor at the rifle ranges where I shot. Watching the flags helped, and when I got my zero, I tried to shoot the same conditions, not always possible in the alloted time frame. Knew of SD, but never really corrected for it.
But, a few weeks ago I took the 7 Rem Mag to a local power line, I can get almost 1900 yrds out of it, for something to do. Had 180 grn. Hybrid Target bullets at 3020 loaded. Set a milk jug at 1k. Conditions were damned near perfect, overcast, very lite wind that looked and felt like it was at 12 O`clock. Ran in my elevation, no wind correction. First shot was just high, but right..with this rifle I can spot my impacts at that distance..corrected with the reticule, 2nd was just left, third was a hit. I`d thought I`d missed wind call my 1st shot, thinking about it now, I believe I missed SD.
Thanks for the explanation.

You sure? I mentioned above to bring up Coriolis Effect. Good read if you care to.

Long Range Shooting: External Ballistics – The Coriolis Effect

There have been so few times I`ve shot in near perfect conditions, that I plum forgot about SD, not to mention Coriolis, and still concentrate on breaking a good shot. Which is another variable in the mix.

Boxers or briefs? Spin or wind? Shoot to the left in the southern hemisphere.

WOW! What a non subject. Edk