Spin Drift

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Back to the dead horse.... ;)

Ballistics programs, such as JBM, will identify spin drift in MOA. You use the drift program and set all wind factors to "0".

Note: All information used to create the chart below are estimations, short of Parker's listed BC for the Black Max and the OP's stated velocity. I do not shoot or have that bullet, so the bullet length I used is the Arrowhead 300gr XLD bullet. Tip length was only guessed.

Obviously environmental factors are likely far from the conditions experienced by the OP.

We know the bullet weight and BC, along with the OP's stated velocity. Bullet length and tip lengths are unknown and only estimated. Not knowing the OP's barrel twist, I used the twist rate of my own barrel of 1:19.

Note....... approximately .5 MOA of drift @ 500yds indicated by the program.





Spin drift check.JPG
 
fourbore said:
Not to beat a dead horse but to show why I made one of my prior statement here is an quote that I believe is accurate:



Note in the above example at 500 yards the drift is 1.5 inch. That would be 0.3 MOA. But out at 1000 yards it is 9 inch. That would be 0.9 MOA. That is 3 time more MOA. Therefor drift should not be expressed as a linear MOA (angle) number. The bullet arcs or curves more and more as it flies. That is why MOA is not generally part of the spin drift vocabulary. What is the MOA on a boomerang?

I can find more source, this was the first I hit with a search that sounded credible:

https://thearmsguide.com/5346/long-range-shooting-external-ballistics-spin-drift-13-theory-section/
Click to expand...
Fantastic post, Thank you
 
ENCORE50A said:
Just great. Now I have to invest in a scope level LOL
Click to expand...

Nightforce makes an AWESOME Set of Rings, With option of a Top Half Bubble Level, About 300 Bucks Worth 😃 RIDICULOUSLY Expensive, But i sure am happy with mine :lewis:

If i already had Leupold Mark 4 Steel Rings, i would go with this Level, i have this one on a Leupold 1” Scope and Really like it, Probably even better than my Nightforce Setup, This is easier for me to Glance at

They make 2 of these, I DON’T Like this one, To BULKY
RJHx03r.jpg


This is the one I REALLY Like, Called their Low Pro 30mm Bubble Level
LXWsUIF.jpg
 
fourbore said:
Not to beat a dead horse but to show why I made one of my prior statement here is an quote that I believe is accurate:



Note in the above example at 500 yards the drift is 1.5 inch. That would be 0.3 MOA. But out at 1000 yards it is 9 inch. That would be 0.9 MOA. That is 3 time more MOA. Therefor drift should not be expressed as a linear MOA (angle) number. The bullet arcs or curves more and more as it flies. That is why MOA is not generally part of the spin drift vocabulary. What is the MOA on a boomerang?

I can find more source, this was the first I hit with a search that sounded credible:

https://thearmsguide.com/5346/long-range-shooting-external-ballistics-spin-drift-13-theory-section/
Click to expand...
This subject of spin drift is very in depth as is everything in long range shooting variables are endless but i will make this statement.

The original post stated very specific question and I gave him a very specific answer with his data based on thousands of rounds fired with a very similar load with several rifles.

Shooting from a bench with a level and with a properly installed scope which is level to the rifle and a dead on 100
Shooting in competition at 100, 200,300,400,500 yds with no sighters or practice we shoot 5 shoots at each target for score no practice. So i found with no wind.
Dead on zero at 100
1/4 moa left at 200 appx 1/2"
1/2 moa left at 300 appx 1 1/2"
3/4 moa left at 400 appx 3"
1 moa left at 500 appx 5"

Is this data linear to 1000yds absolutely not.

But i can assure you with this info from a real world situation and this specific load and properly reading wind and atmosphere.
You can put a shot in the center region of a kill zone or target. Without spin drift data at 500 yds you are out 5" plus any other long range data acquisition errors

So i feel I gave a solid answer to original post
 
ported45 said:
I remember watching a program on Outdoor Channel or Sportsman's that Gunwerks or somebody like that was mounting their scopes with a small degree of crosshair cant that would account for spin drift as the elevation dial was turned.
Click to expand...
How practical & how effective & accurate was that little " hack "?
I've never had the op to shoot out to or past 500yds, so I've never had to learn in-depth about spindrift & how to calculate & effectively compensate for it. But I can tell ya this, canting my scopes crosshair would NOT be how I would personally go about that.
If one is smart enough to calculate their bullets spindrift then calculate the degree of angle to cant their crosshair to essentially " negate " spindrift effectively & accurately at long range, then "dang good on ya". Thats waaaaay over my head.
 
bestill said:
This subject of spin drift is very in depth as is everything in long range shooting variables are endless but i will make this statement.

The original post stated very specific question and I gave him a very specific answer with his data based on thousands of rounds fired with a very similar load with several rifles.

Shooting from a bench with a level and with a properly installed scope which is level to the rifle and a dead on 100
Shooting in competition at 100, 200,300,400,500 yds with no sighters or practice we shoot 5 shoots at each target for score no practice. So i found with no wind.
Dead on zero at 100
1/4 moa left at 200 appx 1/2"
1/2 moa left at 300 appx 1 1/2"
3/4 moa left at 400 appx 3"
1 moa left at 500 appx 5"

Is this data linear to 1000yds absolutely not.

But i can assure you with this info from a real world situation and this specific load and properly reading wind and atmosphere.
You can put a shot in the center region of a kill zone or target. Without spin drift data at 500 yds you are out 5" plus any other long range data acquisition errors

So i feel I gave a solid answer to original post
Click to expand...
Outstanding post. Both times.
 
bestill, I understand now why you properly used the MOA convention. And, I realize that was my confusion not yours around the terminology. And the 5" was a surprise, but; not the first time. In my own defense, I hope that this back and forth helped some others. It got me thinking. I hope it is all good.

I can actually see where a calculator would output MOA. That is how scopes are marked off or adjusted, by angle.
 
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Encore, I have the same (top) Vortex level Lewis displayed that you are more than welcome to should you decide to go that route vice the rings. Luke just installed Hawkins Ultralight Tactical Scope Rings on my build and they have a level as well.
 
fourbore said:
bestill, I understand now why you properly used the MOA convention. And, I realize that was my confusion not yours around the terminology. And the 5" was a surprise, but; not the first time. In my own defense, I hope that this back and forth helped some others. It got me thinking. I hope it is all good.

I can actually see where a calculator would output MOA. That is how scopes are marked off or adjusted, by angle.
Click to expand...
Definitely all good
 
Confusion/Learning continued.... 😄 :snipe:

Interesting the subjects that can come up in the shooting forums, especially the long range forum. ;)
Lots can be learned from just conversing. This has been a good group of posts.

So, I decided to use a bullet that I have in hand and hunt with, the Fury 300gr ST2. Having one in hand with calipers allows me get the measurements needed to throw into JBM's drift calculator. I used mostly my location's information as far as elevation and just threw in a cool 78° temp. BC and velocity for the Fury 300gr ST2 is correct, having verified it on range.

Note............ this velocity is from shooting my custom rifle. The velocity from the BH209 charge I use is very safe in my rifle.

Notice in the chart, all wind settings are set to "0".

At 500yds JBM indicates that there will be 1.1moa of spin drift.

Fury to show spin drift.JPG
 
My best shooting was always prone on the ground. Slightly elevated firing position always helped. I think many long range shooters are more concerned with wind above 1 MPH. Sun position. heat mirage and air temp and some even gun temp. Most will tell you Spin drift is a mute point if they get the range doped out. If I stay on this blog I may send some pictures as soon as I figure it out. I take pride in my guns! And my shooting but my eyes are failing me. But can still hold my own with a scoped rifle.
 
Probably not when shooting the 50BMG on single shot. Believe he was the first ever to attach a scope to one.

RIP White Feather.
 
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fng said:
Probably not when shooting the 50BMG on single shot. Believe he was the first ever to attach a scope to one.

RIP White Feather.
Click to expand...
don't think Carlos had anything to do with it , but maybe Marine Sniper Platoon Hill 55 did. Mounting scope that is
 
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I have a brother that mounted a high power Leupold scope on a English Boys anti tank gun. It was coverted to 50 Cal Browning.
Nothing within a mile was safe.
 

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