Range Report Spin Drift?

camomallninja

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Mar 9, 2009
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Someone told me to get some Spin D! They said it's very refreshing!

I was wondering if any of you guys could share a formula to figure out spin drift.

Thanks
 

VyperCA-941

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May 19, 2012
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Re: Spin Drift?

Drift=1.25(<span style="font-style: italic">Sg</span>+ 1.2)<span style="font-style: italic">ToF</span>^1.83

Where:
<span style="font-style: italic">Drift</span> is spin-drift in inches in the direction of the rifling twist
<span style="font-style: italic">Sg</span> is the gyroscopic stability factor as predicted by the Miller twist rule
<span style="font-style: italic">ToF</span> is the bullet's Time of Flight

Hope that helped?
smile.gif
 

GrantB

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May 23, 2010
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Re: Spin Drift?

A down and dirty formula is 1mph left wind. This will get you close when you are in the field.
 

kraigWY

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Feb 10, 2006
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Re: Spin Drift?

I don't shoot good enough to justify all the math involved while shooting but there is something to it, but I don't think 1 MOA will do it.

Lets take the 30 cal 150 grn ammo at 2700 fps.

In Hatcher-Wilhelm-Malony book on Machine Guns 1917 they delt a bit with spin drift.

At 1000 the above bullet drifted 1 ft
At 1200 it was 2 ft.
At 1400 it was 4 ft.
At 1600 it was 6 ft

It got progressively worse as the range increased, something like 12 at 2000 yards.

Like I said, I have too many other things to worry about when I shoot long range but if one was to take it serious, I'd suggest doing the math an plot it in your data book, adding to you zeros.

Personally I just don't need something else rattling around my head when I shoot.
 

Redmanss

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Aug 24, 2010
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Re: Spin Drift?

I've been looking but can't find Spin-D for sale anywhere. Is there a vendor for it or is it still undergoing FDA testing?
 

MALLARD

none
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Jul 25, 2009
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Re: Spin Drift?

the general rule of thumb

1/2 moa at 1000y
1 moa at 1500y
2 moa at 2000y

is pretty accurate.
 

trevor300wsm

Team Pantydropper
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Nov 8, 2009
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Re: Spin Drift?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Redmanss</div><div class="ubbcode-body">I've been looking but can't find Spin-D for sale anywhere. Is there a vendor for it or is it still undergoing FDA testing?</div></div>

Don't waste your money on Spin-D. Big Rip Off! It's really just yellow #5 mixed with Frank & VJJ's ball sweat. The good stuff is the new and improved formulation of Spin-Xtreme aka "wind grease".
 

Unknown

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Sep 17, 2009
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Re: Spin Drift?

At 600 yards, when shooting my 300 win mag, 190 grain Sierra MK at 2960 FPS, I always have to put in one click left for spin drift. It isn't much, but it is enough to get me from the 10 ring to the X ring. (about 1.5 inches)

Another thing I have to figure in, is that as the barrel heats up (around round 10-12 in a 22 round string:2 sighters, 20 for record) the rounds drift upward. Eventually I figured out that the insulation of the stock on the lower part of the barrel causes the barrel to expand more underneath than it does on top where it gets more air circulation. It works just like the Bi-metal strips used in thermostats.

The lower portion of the barrel retains more heat because of the way the stock keeps air from circulating around it. Therefore, the lower part of the barrel expands more and pushes the rounds upward a bit.

My TRG22 has so much air circulation around the barrel, that it isn't an issue. The McMillan built M40A1 style rifle in 300 win mag has much less air circulation underneath the barrel.
 

kraigWY

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Feb 10, 2006
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Re: Spin Drift?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I've been looking but can't find Spin-D for sale anywhere.</div></div>

You find it at Lowes, in the same asle as the prop dust powder.
 

Redmanss

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Aug 24, 2010
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Re: Spin Drift?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I've been looking but can't find Spin-D for sale anywhere.</div></div>

You find it at Lowes, in the same asle as the prop dust powder.</div></div> Next to the grid squares and PRC-E7's?
 

Killswitch Engage

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Dec 23, 2008
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Re: Spin Drift?

gunny seemed pissed when i told him i was supposed to ask him for a prc-e7.....lmao

good times!
 

Bennyboy

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Dec 30, 2011
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Re: Spin Drift?

When you get to those distances where spin drift is a major concern there are so many other factors (temp, humidity, swirling/angled wind) to insert in the shot.....fact is, there might be a half a dozen people on this forum that could effectually use spin drift to make a "better" shot. Many might include it in their shot calculation, but the vast majority will still have to walk it in....