Spin Drift

Jun 14, 2012
554
3
18
57
texas
#1
I shoot a 6.5CM with a 1:8 twist. At what distance can I expect spin drift to start effecting my shots. Sometimes I don't shoot just to hit the target but I'm shooting for the "X" ring. So I guess I'm asking if wind is no factor, how much will spin drift effect my shots at 600yds and 1000yds? Thanks in advance for any input given.
 

Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
370
114
43
Cedar Springs, MI
#3
Well running solutions in Applied Ballistics app for zero wind with 123 ELD in a 1-8 twist barrel yields the following:
600 : 12.3 MOA,left 0 MOA
600 with spin: 12.3 MOA , left .3 MOA
1000: 30.7MOA, Left 0 MOA
1000 with spin: 30.7 MOA, Left .8 MOA
1250: 48.3 MOA, left 0 MOA
1250 with Spin: 48.3 MOA, left 1.2MOA

Spin drift happens at all ranges so it's technically supposed to be accounted for on every shot but it only starts to be above 1/4moa /.1mil around 500-600 yards. The other issue is that wind is difficult to separate from spin in some cases so it requires a very good wind call/Conditions to see the effect. Not to mention a super precise rifle system including shooter.
 
Likes: SethJ

Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
370
114
43
Cedar Springs, MI
#4
Using same profile as above but with Berger 140 VLD Hunt at 2740fps, gives the following correction values:
600: .3 moa left 1.9 inches
800: .5 moa left 3.9 inches
1000: .7 moa left 6.9 inches
1250: 1 moa left 12.8 inches

Only slightly less drift for the heavier bullet.
 

damoncali

Gunny Sergeant
Mar 19, 2011
1,342
39
48
44
Omaha, Nebraska
#5
If you’re shooting high power (or anything else that allows for sighters) you don’t need to worry about it. It’s going to be almost identical from shot to shot. It only matters when trying to make first round hits without a sighter, and even then most of us aren’t good enough to call the wind tightly enough to see the effect.
 

Bigwheels

Gunny Sergeant
Jun 16, 2007
1,595
56
48
51
Anacortes WA
#6
Several years ago I was shooting to 700yds in an actual 0 wind. It was actually so calm that I had to go down range waving my coat to disperse my smoke after several rnds.
I tried using spin drift in FFS & it put me way right. I was shooting apples off a stump with 0 wind dialed. I've tried it a couple times since & always end up turning it off.
Just my real world observation. YMMV.
 
Likes: Subwrx300

Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
370
114
43
Cedar Springs, MI
#8
I should have added that I was shooting to 600, 800 and 1000 yesterday without spin drift "on" and was still getting solid relatively centered hits in 8-10 mph 9 o'clock hits. I'm still not convinced the effects are large enough to matter in any practical situation. So my experience matches @Bigwheels and @Lowlight .
 
Feb 20, 2013
431
22
18
#9
Most programs calculate SD by following Litz's formula. There is an outstanding paper by Boatright and Ruiz where a new formula is explained and compared to Litz's and 4DOF. The comparisons show how Litz's is a linear value (flat rate) and why it's not right, basically an oversimplification of a very complex factor. I cannot deal with the math myself, but the conclusions are worth reading. All in all, what LL says is demonstrated in the paper.
 

Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
370
114
43
Cedar Springs, MI
#10
Most programs calculate SD by following Litz's formula. There is an outstanding paper by Boatright and Ruiz where a new formula is explained and compared to Litz's and 4DOF. The comparisons show how Litz's is a linear value (flat rate) and why it's not right, basically an oversimplification of a very complex factor. I cannot deal with the math myself, but the conclusions are worth reading. All in all, what LL says is demonstrated in the paper.
Can you send link to that paper, either PM or post?
 

lash

Swamp Rat
Sep 28, 2012
3,042
750
113
59
Central Florida
#11
I should have added that I was shooting to 600, 800 and 1000 yesterday without spin drift "on" and was still getting solid relatively centered hits in 8-10 mph 9 o'clock hits. I'm still not convinced the effects are large enough to matter in any practical situation. So my experience matches @Bigwheels and @Lowlight .
Can you send link to that paper, either PM or post?
Yes, please. If you have a link, I can add it to the resources here on the hide, to go along with a few other papers by Jim Boatright
 

SethJ

New Hide Member
#12
I don't correct for it at 1000 yards with my 6.5,....haven't noticed a problem. My groups aren't small enough to even worry with it though. At 1000 yards,...on a good day I might do a 10" group..so many other factors affect my shots like WIND being the biggest,..I just don't worry with spin drift.I guess if I was shooting 1500 yards I'd have to do something about it, but heck how often,..or how many people really have that distance available to even shoot at.
 

THEIS

Sergeant of the Hide
Nov 27, 2017
621
861
93
#15
Can you send link to that paper, either PM or post?
Hi,

I tried attaching here and uploading to the resource section but for some reason I cannot get past 10% loading. If you google search Calculating Yaw of Repose and Spin Drift it should come right up for you or I can email it to you.


Edited...Upload to resources worked this time :)

Sincerely,
Theis
 
Last edited:
Likes: LastShot300

Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
370
114
43
Cedar Springs, MI
#16
Hi,

I tried attaching here and uploading to the resource section but for some reason I cannot get past 10% loading. If you google search Calculating Yaw of Repose and Spin Drift it should come right up for you or I can email it to you.


Edited...Upload to resources worked this time :)

Sincerely,
Theis
Awesome! Thank you Theis!
 

Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
370
114
43
Cedar Springs, MI
#17
Hi,

I tried attaching here and uploading to the resource section but for some reason I cannot get past 10% loading. If you google search Calculating Yaw of Repose and Spin Drift it should come right up for you or I can email it to you.


Edited...Upload to resources worked this time :)

Sincerely,
Theis
Just read through paper briefly and, please check my understanding: the newer model and PRODAS simulations were in very high agreement with each other. The Litz Model is within 2-10% of the other three models listed (depending on bullet stability and bullet type). Compared to Litz Model, it seems that the major difference is primarily shown in lower stability scenarios whereas high stability/lower drag bullets are still within +-2% of other models. Newer models show a 2-5% reduction in effect as compared to Litz Model.

If I'm reading that correctly, then it's not that spin drift is substantially over calculated or over accounted for but rather newer models show 1-3" less drift at 1000 yards. In either case it still means that SD should be accounted for when deriving a first round hit solution as it is still an appreciable amount under either model. Both models show SD of 9-10" for a VLD bullet at 1k which is important for creating first round impact.

Does that seem about right as far as summary?
 
Feb 20, 2013
431
22
18
#18
Just read through paper briefly and, please check my understanding: the newer model and PRODAS simulations were in very high agreement with each other. The Litz Model is within 2-10% of the other three models listed (depending on bullet stability and bullet type). Compared to Litz Model, it seems that the major difference is primarily shown in lower stability scenarios whereas high stability/lower drag bullets are still within +-2% of other models. Newer models show a 2-5% reduction in effect as compared to Litz Model.

If I'm reading that correctly, then it's not that spin drift is substantially over calculated or over accounted for but rather newer models show 1-3" less drift at 1000 yards. In either case it still means that SD should be accounted for when deriving a first round hit solution as it is still an appreciable amount under either model. Both models show SD of 9-10" for a VLD bullet at 1k which is important for creating first round impact.

Does that seem about right as far as summary?
In general terms, the paper shows what you say. However the point remains the same.

Simply because for some bullets at a certain Sg range Litz can work, but in most cases the SD is over valued, therefore I cannot trust in a model where I cannot anticipate when and how it will properly work, would you? I for sure, don't like to play the ELR game tossing coins in the air when the chips are down.
 
Feb 20, 2013
431
22
18
#19
Yes, please. If you have a link, I can add it to the resources here on the hide, to go along with a few other papers by Jim Boatright
There is another paper by Jim and Gus on Aero Dynamic Jump, where a new math is developed and compared to Litz's AJ formula. Both papers (SD and AJ) were posted in the old forum last year. Once again, Litz's formula is an over oversimplification of the real world for the worst.
 

Lowlight

HMFIC of this Shit
Staff member
Apr 12, 2001
26,724
1,800
113
Base of the Rockies
www.snipershide.com
#20
It's wrong,

On an 18" wide target where you are aiming in the center, not using any SD is a Miss, according to the numbers, that rarely happens,

The real world, it's like 3" at 1k, not 9"

This is where the science is not exact, if 9" was correct, everyone would see it, and that just doesn't happen. The USMC made them remove it, it was never talked about, does not exist in the manuals and we graduated SS school never touching it. No CE, No SD, no problem.

I get plenty of 1st round impacts and leave it off ... if you look at a lot of the Hornady 4DOF number 1 MOA does not happen until close to 1500 yards in our current calibers. Their reference data is based off a 168gr out of a 30-06 going 2550fps or something close to that.

They add in a flat rate number based on TOF and call it good, that is not correct.

3" in the real world
 

tna9001

Sergeant of the Hide
Aug 4, 2017
332
87
28
#27
It's wrong,

On an 18" wide target where you are aiming in the center, not using any SD is a Miss, according to the numbers, that rarely happens,

The real world, it's like 3" at 1k, not 9"

This is where the science is not exact, if 9" was correct, everyone would see it, and that just doesn't happen. The USMC made them remove it, it was never talked about, does not exist in the manuals and we graduated SS school never touching it. No CE, No SD, no problem.

I get plenty of 1st round impacts and leave it off ... if you look at a lot of the Hornady 4DOF number 1 MOA does not happen until close to 1500 yards in our current calibers. Their reference data is based off a 168gr out of a 30-06 going 2550fps or something close to that.

They add in a flat rate number based on TOF and call it good, that is not correct.

3" in the real world
Is the 3" number from the other methods to calculate SD? Is that using the above-mentioned load?
 

Lowlight

HMFIC of this Shit
Staff member
Apr 12, 2001
26,724
1,800
113
Base of the Rockies
www.snipershide.com
#28
SD goes beyond the rifle twist rate,

The bullet length matters, the amount of spin, the velocity, the point of the trajectory you are measuring it, the wind, not just the wind speed but the wind direction. Actually, the entire bullet design has a factor in it. From nose to tail as well as the groove design.

Most Apps are not "calculating" anything, you need specific data along with a 6DOF to figure out the actual prediction, and those predictions don't include all the above. They just use some basic data and a flat rate value. That value is normally set to equal 1 MOA at 1000 yards with a specific TOF. In other words:

They figure everything that crosses the same point at the same time is drifting the same amount. By doing it this way they feel it helps more than it hurts, and that adding in something is better than adding nothing. I have seen this bit people more so than doing nothing because it changes your wind call.

Get better at calling the wind, and ignore SD.

Some apps you can change your zero range to say, 600 yards and the SD will be the same as if you have a 100 yard zero. We've played with that and demonstrated the flaw in the system

SD is more a buzzword than an actual thing you have to worry about. It gets lost in a lot of noise of the shot, from poor trigger control pulling the shots right (Most people are righthanded, add in a left-handed shooter and you'll see a difference) to blown wind calls, to variations in the bullet vs rifle twist.

I don't know how many times I have to repeat myself, a lot of us never use it and never see a negative effect on our end results. Doesn't get any easier. if it was an actual issue we'd all be using LH Twist Barrels in the USA as a routine to reduce it to a microscopic number. We don't because it really really doesn't matter.

Dope the wind inside 1500m and don't worry about the tiny things.

Here is the deal, don't listen to me, read it yourself, you can find it in more than one book

IMG_0269.JPG
IMG_0270.JPG
 
Jun 26, 2012
2,213
929
113
N. Carolina
#38
OMFG!! MY wife she works all day with CNN playing..has become totally anti-gun... Pissed about our son shoots matches with me-(used to like it)-

But she LOVES sparkling water - Way over priced , but She'll be drinking SD for a while .. Guess what.. this will be my personal inside joke!! THANKS!!

View attachment 6884191
you know, this just proves why capitalism works and why i hate communists.
 

sandwarrior

Gunny Sergeant
Apr 21, 2007
4,309
227
63
in yooperland
#39
OMFG!! MY wife she works all day with CNN playing..has become totally anti-gun... Pissed about our son shoots matches with me-(used to like it)-

But she LOVES sparkling water - Way over priced , but She'll be drinking SD for a while .. Guess what.. this will be my personal inside joke!! THANKS!!

View attachment 6884191
You forgot:
Wife drinking it and not knowing what Spin Drift means in the shooting world: .....PRICELESS!!

:D:eek::cool:
 
Likes: Bender

TripleBull

This one goes to 11
Feb 13, 2017
2,057
3,140
113
#40
OMFG!! MY wife she works all day with CNN playing..has become totally anti-gun... Pissed about our son shoots matches with me-(used to like it)- But she LOVES sparkling water - Way over priced , but She'll be drinking SD for a while .. Guess what.. this will be my personal inside joke!! THANKS!!
I think we have right here, theoretical proof that spin drift is more powerful at drifting forum threads than projectiles.

Diver, I feel for you, man. My wife is so pro-gun redneck killem all beat their ass, I have to stay on my game to lead the family.

Stay strong, brother.
 

Skookum

Knuckle Dragger
May 6, 2017
362
239
43
#44
SD goes beyond the rifle twist rate,

The bullet length matters, the amount of spin, the velocity, the point of the trajectory you are measuring it, the wind, not just the wind speed but the wind direction. Actually, the entire bullet design has a factor in it. From nose to tail as well as the groove design.

Most Apps are not "calculating" anything, you need specific data along with a 6DOF to figure out the actual prediction, and those predictions don't include all the above. They just use some basic data and a flat rate value. That value is normally set to equal 1 MOA at 1000 yards with a specific TOF. In other words:

They figure everything that crosses the same point at the same time is drifting the same amount. By doing it this way they feel it helps more than it hurts, and that adding in something is better than adding nothing. I have seen this bit people more so than doing nothing because it changes your wind call.

Get better at calling the wind, and ignore SD.

Some apps you can change your zero range to say, 600 yards and the SD will be the same as if you have a 100 yard zero. We've played with that and demonstrated the flaw in the system

SD is more a buzzword than an actual thing you have to worry about. It gets lost in a lot of noise of the shot, from poor trigger control pulling the shots right (Most people are righthanded, add in a left-handed shooter and you'll see a difference) to blown wind calls, to variations in the bullet vs rifle twist.

I don't know how many times I have to repeat myself, a lot of us never use it and never see a negative effect on our end results. Doesn't get any easier. if it was an actual issue we'd all be using LH Twist Barrels in the USA as a routine to reduce it to a microscopic number. We don't because it really really doesn't matter.

Dope the wind inside 1500m and don't worry about the tiny things.

Here is the deal, don't listen to me, read it yourself, you can find it in more than one book

View attachment 6884151
View attachment 6884152
This passage you show in the attachment is talking about Coriolis effect. You do realize that gyroscopic procession (spin drfit) and coriolis are not the same thing right?
 
Nov 25, 2010
199
9
18
ME
#50
I'll never enjoy that can of tart hipster seltzer the same way again--too funny. They should spiral the grapefruit like Bartlein's logo...
 
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