Spin Drift Data

[CharlieNC]

My app shows .2 to .3 mil spin drift at 1000yd, and for smaller targets this is significant. Has anyone seen actual sd data reported, ie in a wind free tunnel, or is the calculation more theoretical. Many will argue sd is insignificant and can be ignored, but informed shooters just need to know (forget the add that line came from).

 

[_Windrider_]

Bryan litz has done a lot with this. I sure you've heard of him. I used my Google fu and quickly found this

http://www.appliedballisticsllc.com/...ndCoriolis.pdf

simple physics tells you that a spinning object produces lift (how else would a helo fly) so not accounting for it in a spinning biller would have consequences.

 

[CharlieNC]

Yes I have this book. I understand the concept, but am asking about actual data whereby this was measured. Data abounds regarding trajectory and velocity curves which are used to allow us to accurately calculate drop, and most shooters do well handling elevation. Wind is the nemesis, and sd is a confounding factor. Shooting a match Sat where one target is smaller than the calculated sd! My experience suggests the sd effect is over calculated, since center holds on 1000yd targets yields hits when there appears to be "no" wind.

 

[JMGlasgow]

https://youtu.be/yvl_W-XVXD0

 

[jbailey]

Got to ask what load has you with .2 to .3 mils of spin drift and are you sure you are calculating the correction the right way? That is a lot of drift. My 6x47 105gr load, launching at 3050fps from a 7.5 twist drifts 0.16mil according to my Kestrel AB (and JBM) ... I usually put on 0.1L and I'm fine.

 

[CharlieNC]

JM the funny part is the high sd is calculated by Trasol, the best! JB this is for high bc/high velocity in 6.5 and 223. Other calculators do not give this much sd, and for these types of disagreements a little data would help.

 

[_Windrider_]

Data from a windless tunnel would b difficult to attain. It would have to be a massive tunnel first of all. But spin drift is fact based on basic physics. It's effect however is different for every bullet and typically isn't a huge factor until we are reaching medium ranges and beyond, say 800 yds or more (again depending on bullet. A .308 at 800 will have a lot more SD at 800 than your 6.5CM). It's a function of stability and speed. It exists because we know the tip of the bullet isn't pointed directly at the target while in flight (yaw of repose). Generally the more stabilized a bullet is the less the effect. Fast twist rate and higher MV with a good BC will minimize its effect. The trick is to find the best combo of those for the application you are using it for. On a .308, it is something in the realm of 10" of drift at 1000yds. Probably way less for the faster higher BC 6.5CM.

 

[Lowlight]

The old SD data published is flat out WRONG !

I don't care how many times they write it, they are wrong, it is a lot less than advertised, they are guessing.

You need not bother with SD inside 1500 yards with any caliber, it's that simple

They use SPARK Range data for SD, and that very limited, but shows there far less than advertised.

It's always the people with the least amount of experience putting the highest premium on what they read about SD and CE

 

[_Windrider_]

The old SD data published is flat out WRONG !

I don't care how many times they write it, they are wrong, it is a lot less than advertised, they are guessing.

You need not bother with SD inside 1500 yards with any caliber, it's that simple

They use SPARK Range data for SD, and that very limited, but shows there far less than advertised.

It's always the people with the least amount of experience putting the highest premium on what they read about SD and CE

You've been pretty quiet on the TRASOL thread so I'll aske here, what's going on with it? Is it dead or just on the back Burner?

 

[damoncali]

Yes, you can measure it, but it's a small effect and it's difficult to do. You can use radar data and try to separate out the other effects, which is hard, or you can measure lift in a lab, and try to figure out yaw of repose somehow, which will also get you there. Bottom line: it's real, it's small, and it can almost always be ignored. The one exception (arguably) being first round hits at extremely long range (think king of 2 mile type competitions), and even then, there are a whole host of things that matter a whole lot more. It's not something worth worrying about.

 

[CharlieNC]

So there is no empirical verification at all for an app such as Trasol? It would be nice if the sd calc could be turned off.

 

[_Windrider_]

So there is no empirical verification at all for an app such as Trasol? It would be nice if the sd calc could be turned off.

You can in applied ballistics mobile, also in ballistic AE if I'm not mistaken. I was messing with this on my way to Seattle last night and AB had it at .1mils at 1000 for my 6.5cm. Like lowlight said it's not an issue except in true ELR.

 

[Rthur]

Sweet Jesus, make it stop...

R

 

[Darkside-Six]

So there is no empirical verification at all for an app such as Trasol? It would be nice if the sd calc could be turned off.

You can turn it off. Go to settings and switch it to off.


Sent from my iPhone using Tapatalk

 

[MilDot1960]

My App is saying 0.18 Mils at 1000yds for SD which is -6.6 inches on a .308 175gr RDF. ? So I am wondering why should we ignore it under 1500 if it's Aiming 6.6 inches to the right at 1 K

here's what I get

SD = -1.8 = -6.6" ' 1k

Cori = -0.09 = -3.2" @1k

SD + Cori = -0.27 Mils = -9.8 Inches @ 1k.

John.