Spin Drift

Downeast

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I know, a terrible phrase to hear. At 1,000 yards should this become a major factor? I did some calculations using one of the online ballistic calculators and the spin drift was over 6 inches at 1k based on my input variables. The reason I ask is that I tended to hit to the right of center. The very bottom hit was done by a friend with a different rifle. It was his first hit ever at 1,000 yards. Very little wind (based on flags along range) and the rifle was dead on at 200 yards. Quite a bit of mirage though. I'm still learning this long range stuff so please bare with me. 1000 yard Karson City.jpg
 
If that's a 12" plate...and your calcs called for spin drift of 6", I'd say that's dead on! Great shooting.
 
I guess the "group" would be close to 12 inches??
 
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I did some calculations using one of the online ballistic calculators and the spin drift was over 6 inches at 1k based on my input variables
I think you answered your own question. The center of your group is about 6" right of center. That's some fine shooting!
 
Spin drift is going to be controlled by several factors:

Amount of spin- how many revolutions per foot from the rifling,

Length of barrel

Weight and shape of projectile

Distance

Corriolis effect
 
6" at 1000yds is about 1/2 moa.

So many factors can cause a 1/2 moa shift that spin drift is very minor.

When you get so damn good that you factor in spin drift, just add 1/2 moa or .1mil left and BAM no more spin drift.
 
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What are you shooting? Caliber, barrel lenght.

Savage 112 in .338 Lapua, 300 Berger OTM (BC= 0.82), 26 inch barrel. If the winds die down I'm going to go back out there and add 0.1 mil left and see what happens.

I'm going to try the 6.5 Creedmoor next with 142 Sierra HPBT. It's shooting less than 1/2 moa as well. Thanks for the help and comments. My wife takes the pics of the target from 200 yards away since I have to wade across two creeks to get to it. :mad:
 
My first thought was that hitting the plate at all with that much breeze was pretty impressive. Then I got to wondering if it was hung on the limb. Hard to tell. Still, nice shooting.

Edit: Can you see the ribbon in the scope at 1K?
 
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You can barely see it and then only if it is moving in the wind. The target is hung between two trees from a cable and we bolted an old boat winch to one of the trees to raise and lower it. It is attached to the cable with two pieces of fire hose. The only problem is that is is hanging over a creek so when you repaint it you have to lower it and then wade out to paint it. The plate is 1/2 inch steel and quite heavy. Even with the 338 LM you can barely hear the ding and it doesn't seem to move at all. We plan on replacing it this coming week with two old 20 inch round discs stacked together hoping that they will make more noise and maybe move enough to see a hit. This is ain't your normal range. You have to be able to walk, climb over storm debris, clear brush, wade through muck and several creeks and fight off the bugs and the occasional cottonmouth. If it stays dry for another week or two I may be able to even use my 4 wheeler again. At least to the 800 yard line. After that it's chest waders and decoy sleds. It's a tough place to shoot but it's ours and no one bothers us.
 
Spin drift and Coriolis in the northern hemisphere account for 11.5" shift of impact to the right at 1000yds...per Bryan Litz
http://www.appliedballisticsllc.com/Articles/ABDOC108_GyroscopicAndCoriolis.pdf

Coriolis,
West only, east is less, north and south are 0 value. its a value of 1/8 moa. Keep in mind that value of 1/8 moa is west driven. But if you are a touch off at a angle you wiggle ones ability to more 0 then greater then 1/8th moa.

Back to spin drift, a click left fixes it. Same with Coriolis so make two clicks left

Best option is quite installing Right hand twist and flip the barrel around go nuts!!?? Backwards baby!!!!! Get you a super dave crazy wild "left twist". Oh my....
 
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