SPIN DRIFT!....I'm such a dummy

[J E Custom]

When Shooting 500 to 1000+ yards I recommend making the vertical (MOA) adjustments, then the
spin drift(MOA) adjustments needed at that range and them do the actual wind (MOA) adjustments
for the conditions.

This basically sets the zero under a no wind condition before the wind is be added.

There was also the mentioning of mirage. If you can read it you should set the approximate
mirage effect before starting the elevation adjustments.

This will improve the chance of a good cold bore shot. If you set all of these factors before
firing the first sight-er(Shooting target matches) it will minimize the sight correction needed.

Spin drift is just like the Coriolis effect it does not make much difference at 400 or 500 yards
but at 1000+ it starts having an effect on the bullet that can spoil a shot.

To me Coriolis is the tough one to figure out because it is also affected by the direction that the
shot is fired compared to the rotation of the earth.

Good Thread !!!!!!!

J E CUSTOM

 

[Michael Eichele]

Spin drift is just like the Coriolis effect it does not make much difference at 400 or 500 yards
but at 1000+ it starts having an effect on the bullet that can spoil a shot.

To me Coriolis is the tough one to figure out because it is also affected by the direction that the
shot is fired compared to the rotation of the earth.

Good Thread !!!!!!!

J E CUSTOM

Coriolus has less to do with the direction of fire and more to do with which hemisphere you are in and how far or close you are to the equator. The vertical component has a fair bit to do with your direction of fire. The horizontal component has to do with how close you are to which pole. Northern hemisphere shooters will see right hand impacts and SH shooters will see left hand impacts which out to 1K is minimized from using a right hand twist barrel. In the NH, we see coriolus AND spin drift combined.

Too bad someone reputable doesnt produce a left hand twist barrel for us NH shooters.

One of the best animations illustrating the right hand NH impact vs left hand SH impact is below:

http://www.youtube.com/watch?feature=player_detailpage&v=__SlJtnpCD8

http://www.youtube.com/watch?feature=player_detailpage&v=mcPs_OdQOYU

 

[J E Custom]

Coriolus has less to do with the direction of fire and more to do with which hemisphere you are in and how far or close you are to the equator. The vertical component has a fair bit to do with your direction of fire. The horizontal component has to do with how close you are to which pole. Northern hemisphere shooters will see right hand impacts and SH shooters will see left hand impacts which out to 1K is minimized from using a right hand twist barrel. In the NH, we see coriolus AND spin drift combined.

Too bad someone reputable doesnt produce a left hand twist barrel for us NH shooters.

One of the best animations illustrating the right hand NH impact vs left hand SH impact is below:

YouTube - EFECTO CORIOLIS

YouTube - coriolis effect (2-11)

Exactly !!!! that's why I said it was difficult to calculate for each shot. Even your explanation sounds
difficult to understand.

And as you know if you fire a projectile along the equator, Coriolis has no effect "BUT"
if you fire it north or south it has the most effect, So each shot is somewhere in between
and must be calculated for that angle to get a correction.

The best description of Coriolis is Leade just like a running target. The problem is in the correct
calculation.

Also the Brits have been using left hand twist a loooong time.

I wonder if they knew something about it back then. They did have a 2000 yard match.

J E CUSTOM

 

[Buffalobob]

A little funny story--

I was out antelope hunting last year and had the amount of spin drift on my drop chart. I was bored sitting there and got to looking at the drop chart and suddenly realized I could not remember whether spin drift was left or right.

 

[Bobcape]

Thanks for posting thses links. Very useful addition to Bryan Litz' book.

Bob

Coriolus has less to do with the direction of fire and more to do with which hemisphere you are in and how far or close you are to the equator. The vertical component has a fair bit to do with your direction of fire. The horizontal component has to do with how close you are to which pole. Northern hemisphere shooters will see right hand impacts and SH shooters will see left hand impacts which out to 1K is minimized from using a right hand twist barrel. In the NH, we see coriolus AND spin drift combined.

Too bad someone reputable doesnt produce a left hand twist barrel for us NH shooters.

One of the best animations illustrating the right hand NH impact vs left hand SH impact is below:

YouTube - EFECTO CORIOLIS

YouTube - coriolis effect (2-11)

 

[Michael Eichele]

JE,

I wasnt trying to undermine anybodies abilities or intelegence. Im sorry if I came accross that way.

I guess what I was trying to get at was that right coriolus shouldnt be difficult to figure out. To the best of my knowledge, the left or right hand impact are very consistent regardless of direction of fire. Once you figure out how much, you can use that value regardless. Now if we are talking a due east or due west shot, then there is a vertical component which I understand to be very minimal. I also believe that the closer you are to the poles, the greater the effect. Again, regardless of the direction of fire.

I may be wrong about this who knows? Maybe someone who really knows their physics can chime in. Maybe I will learn something.

Now if we could just get an AMERICAN barrel maker to make left hand twists.............

M

 

[J E Custom]

JE,

I wasnt trying to undermine anybodies abilities or intelegence. Im sorry if I came accross that way.

I guess what I was trying to get at was that right coriolus shouldnt be difficult to figure out. To the best of my knowledge, the left or right hand impact are very consistent regardless of direction of fire. Once you figure out how much, you can use that value regardless. Now if we are talking a due east or due west shot, then there is a vertical component which I understand to be very minimal. I also believe that the closer you are to the poles, the greater the effect. Again, regardless of the direction of fire.

I may be wrong about this who knows? Maybe someone who really knows their physics can chime in. Maybe I will learn something.

Now if we could just get an AMERICAN barrel maker to make left hand twists.............

M

Thanks :but I wasn't offended . It is a discussion and open for comments and the more
we get hopefully the more we learn.

There are a lot of things that I am not an expert about and this is one of them. I do know
that you almost have to have a computer to figure coriolus effect.

I have heard the theory behind having a right hand twist is to prevents the barrel from
trying to unscrew upon firing.

I have not seen this happen to a left hand twist barrel but if anyone has please comment.

J E CUSTOM

 

[jonoMT]

Augustus, that's funny because I just came across that thread on the 'Hide while looking for info on spin drift. Certain individuals were adamant about it not being at all important...until Litz reluctantly entered the fray and posted a thoughtful explanation about its reality. I can agree with those who don't care to an extent. It's way down the list of things I worry about, like trigger control, when shooting at long range. But why not have the best theoretical approximation you can start with?

As far as handheld calculators go or even generating a drop chart to print out, it's just as well to add spin drift in there. As for the Coriolis Effect, I read Ch. 7 in Litz book and decided it wasn't worth worrying about as much since the effect is less and the need for input is greater. But with a device that has location info and azimuth, why not?

 

[elkaholic]

How much of this is caused from twist vs. coriolis??.........Rich

 

[Michael Eichele]

How much of this is caused from twist vs. coriolis??.........Rich

It will vary from caliber to caliber and distance to distance but for the distances most shooters here stay within 95% of the right hand drift will be due to spin drift. Up to 1K my opinion is that coriolus is very minimal. It is fun to talk about and cool to debate but when it comes right down to it, coriolus has little to do it. At 3000 yards, it may be a different story.

I am no expert on this subject so I could be totally wrong here. It is my opinion only.

M

 

[RoyB]

I've always known about SpinDrift, but was more concerned with a scope that was set up PERFECTLY in line with the bore of the rifle. I always felt if the scope wasn't set up perfectly, this would cause more left and right inaccuracy at long range than just about anything else.

And then I started to figure, if we could measure the amount the scope was out of alignment with the bore, we could offset it to compensate for SpinDrift...........

I've never seen or heard of an exact method to align the scope with the bore.

Comments?

 

[paphil]

Spin drift is something that really needs to be addressed in long range shooting. I don't consider myself to be any kind of expert but I did kill about 500 groundhogs here in Pa. this past year , most from 500 to 800 yards and only one at 1000 yards. Ignoring spin drift is a sure miss at longer ranges on small targets. A very useful piece of information on spin drift is pointed out by John Porter in the dope the wind vidio. The drift is right or left depending on the twist of the barrel but also up or down depending on the wind direction! It is about a 3-3 1/2 to1 ratio. So on a right twist barrel with a left to right wind with a hold value of 3 minutes, the impact at 1k will be 4 min right and about 1 1/3 min low. (3 min wind + 1 min spin) On the other side, with a 3 min right to left wind, the POI will be 2 min left and about 3/4 min high. I got pretty good at reading the wind but couldn't figure out the high and low misses untill I saw the vidio. I'm shooting a 22-243 with a 1in8 twist Hart barrel and have shot 3 shot groups at 300 yards that measure less than 1/2 inch . I've heard that stupidity is repeatedly doing the same thing and hoping for different results and that is what I do when I expect to hit that cold bore target and don't take into consideration all the variables. I'll find out this summer when I add in the additional inputs. This 10:00 / 4:00 slope with the wind is built in on the new Huskamaw reticles.

 

[xfyrfiter]

I used to shoot 1K BR and it seemed that the heavier calibers had more drift than lighter ones. Just my observation and I dont think I have ever seen a wind free day at the range

 

[load]

It will vary from caliber to caliber and distance to distance but for the distances most shooters here stay within 95% of the right hand drift will be due to spin drift. Up to 1K my opinion is that coriolus is very minimal. It is fun to talk about and cool to debate but when it comes right down to it, coriolus has little to do it. At 3000 yards, it may be a different story.

I am no expert on this subject so I could be totally wrong here. It is my opinion only.

M

it will also vary depending on bullet length vs rifle twist. a short bullet spun at a 1 in 9 will "stand up" more than a longer bullet will when spun and the same rate. the key to minimizing the effect is to fire a ballistically balanced bullet/twist/volocity that will point as directly at the target as possible while still remaining stablegun)
as for corialis i usually input 1/4 moa left for 1000 1/2 left for 1500 and 3/4 left for 1760 assuming 45 degree lat. directly east/west shooting just remember the target is rising to you when shooting west you'll shoot low so adjust up 1/4@1000 1/2@1500 3/4@1760 and opposite for east shooting. for east/south or west/north or any other combo simply dividing into 3 sectors will get you close enouph so lets say you nnw@1760 yrds you'd only have to vertically adjust as close to 3/16 moa up while nw would be as close to 3/8 moa and wwn being 5/8. of course this is not perfect it works for as closer than you can dial again assuming 45 degrees lat. this assumes 2850 fps mean volocity and a bullet with a 5.75 bc
clear as mud