"Spin-drift", gyroscopic drift, and/or Coriolis effect and p

[ChristianHE]

Need some input, advice, experiences, info, etc. about "Spin-drift", gyroscopic drift, and/or Coriolis effect and precession etc. Long post, bear with me! I did search and didn't find really what I was looking for, especially one thread that really drifted!

According to the info I've found so far, the spinning of the bullet (out of my RH twist barrel) causes the nose to angle a little to the right and maybe even up, causing a curve in the flight to the right. Also, I just talked with a shooter from Ft. Benning who shot a match with us who told me about bullet flight time and the Coriolis effect. He shoots a .338 Lapua Mag sometimes over a mile, and had dope in his book for his gear but of course not for mine. (19.5" 6.5Grendel 1in8 twist, my favorite load is Nosler CustomComp HPBT 140gr with CCI#450, and 28.5 gr Accurate 2520, MV right at 2400)

I've been shooting at a range where I can do 200, 300, 400, 500, 600 all on the same line in the same direction, which is just about due North. I've had it to myself a couple times and been able to drive down to my targets!

The previous times I've shot these distances there has been wind, from 5-7mph, sometimes 10-15mph, always from the West, so Left to Right as the range faces almost due North.

I have a really tight 200 yard zero, which I verified every time. I use hold-overs in my NightForce 1-4 NXS MilDot scope. in the 1st Mil dot at 300, 1.5 at 350, 2nd at 400, 3.5 at 500 and a little less than the 5th Mil dot at 600.

THIS TIME I went and there was ZERO wind, not even a breath, a dead calm morning in FL. About 80 degrees, 78 feet elev (according to my Garvin Nuvi GPS) 86% humidity, steady barometer. I always attributed the gradual movement of my groups to the right the further away I shot to be the wind, and never even heard of gyro-anything or coriolis and flight time until this Active duty guy mentioned it when I told him about this. After seeing the same thing (perfect at 200 and 300 then each group moving further right past 400, to 6-1/2 to 7 inches at 600 yds) WITH ZERO WIND got me thinking.

Since my scope is factory set for about 250 yd parallax, is that maybe the problem not any of the above? Or are "Gyroscopic drift" and Coriolis factors here? Maybe my scope is not mounted with the vertical reticule exactly vertical to the bore so the further out the more it is effecting my group placement? I'm happy with the groups, 6-8" at 600 but I don't like having to hold a little left to get them center target...

Wiki pedia has this, but I don't see the source and am not sure what to think:

Gyroscopic drift (Spin drift)

Even in completely calm air, with no sideways air movement at all, a spin-stabilized projectile will experience a spin-induced sideways component. For a right hand (clockwise) direction of rotation this component will always be to the right. For a left hand (counterclockwise) direction of rotation this component will always be to the left. This is because the projectile's longitudinal axis (its axis of rotation) and the direction of the velocity of the center of gravity (CG) deviate by a small angle, which is said to be the equilibrium yaw or the yaw of repose. For right-handed (clockwise) spin bullets, the bullet's axis of symmetry points to the right and a little bit upward with respect to the direction of the velocity vector as the projectile rotates through its ballistic arc on a long range trajectory. As an effect of this small inclination, there is a continuous air stream, which tends to deflect the bullet to the right. Thus the occurrence of the yaw of repose is the reason for bullet drift to the right (for right-handed spin) or to the left (for left-handed spin). This means that the bullet is "skidding" sideways at any given moment, and thus experiencing a sideways component.

The following variables affect the magnitude of gyroscopic drift:

Projectile or bullet length: longer projectiles experience more gyroscopic drift because they produce more lateral "lift" for a given yaw angle.

Spin rate: faster spin rates will produce more gyroscopic drift because the nose ends up pointing farther to the side.

Range, time of flight and trajectory height: gyroscopic drift increases with all of these variables.

Doppler radar measurement results for the gyroscopic drift of several US military and other very-low-drag bullets at 1000 yards (914.4 m) look like this:

Bullet type US military M193 Ball US military M118 Special Ball Palma Sierra MatchKing LRBT J40 Match Sierra MatchKing Sierra MatchKing LRBT J40 Match LRBT J40 Match

Projectile weight (in grain) 55 gr 173 gr 155 gr 190 gr 220 gr 300 gr 350 gr 419 gr

Projectile diameter (in inches and mm) .223 in / 5.56 mm .308 in / 7.62 mm .308 in / 7.62 mm .308 in / 7.62 mm .308 in / 7.62 mm .338 in / 8.59 mm .375 in / 9.53 mm .408 in / 10.36 mm

Gyroscopic drift (in inches and mm) 23.00 in / 584 mm 11.50 in / 292 mm 12.75 in / 324 mm 3.00 in / 76 mm 7.75 in / 197 mm 6.5 in / 165 mm 0.87 in / 22 mm 1.90 in / 48 mm

The table shows that the gyroscopic drift is rather variable and no clear trend is easily distinguishable.

[Boats]

I will take a stab at answering. I am not a "sniper" but have shot a lot of mid range rifle, out to 600 yards. Modern Rifles over the course with iron sights, Silouette scope sights and Black powder cartridge guns with tang sights. A very little bit of 1000 yard shooting mostly with Black powder guns.

Most rifles will have different windage "mechanical" zeros as distances increase. It's fairy difficult to get your sight to track exactly plumb as it elevates. Scopes same thing if they are not mounted exactly square, very little cant will cause it to track off. You see this most often with tang staff sights on Black powder cartridge guns that require a lot of movement because of the bullets high trajectory. With a high velocity gun it's not as obvious. The bullet will also drift as distances increase more with slow heavy ones than light fast bullets. Last don't forget your head positon and cheek pressure is different as you shoot longer range targets with Iron sights and they elevlate. This can have signifigant effect on zero. Again high velocity and scopes it's not as obvious

I have a table of sights for all my match rifles with elevation and windage zeros for distance. Have looked at scopes that have mill dots for elevation. Used to have a varmit Unertil with two elevation cross hairs Idea was to bracket the varmit. Thing always confused me and caused misses, and am sure all those dots would do the same thing. Single Dot reticule, table of sights pasted to the stock, click in the settings for distance and windage is best for me.

Boats

[Jadeslade]

Probably something else going on than gyroscopic effect-bullet design minimizes this for specific velocities and distances, which I am sure you are operating in. The Coriolis force operates on really large forces. If you were shooting ICBMs and the like. Agree with Boats-might be verticality and smaller stuff, I wouldn't worry about gyroscopic and Coriolis forces for your shooting. Now I know what those whizzing sounds are past my window!

[ChristianHE]

I will take a stab at answering. I am not a "sniper" but have shot a lot of mid range rifle, out to 600 yards. Modern Rifles over the course with iron sights, Silouette scope sights and Black powder cartridge guns with tang sights. A very little bit of 1000 yard shooting mostly with Black powder guns.

Most rifles will have different windage "mechanical" zeros as distances increase. It's fairy difficult to get your sight to track exactly plumb as it elevates. Scopes same thing if they are not mounted exactly square, very little cant will cause it to track off. You see this most often with tang staff sights on Black powder cartridge guns that require a lot of movement because of the bullets high trajectory. With a high velocity gun it's not as obvious. The bullet will also drift as distances increase more with slow heavy ones than light fast bullets. Last don't forget your head positon and cheek pressure is different as you shoot longer range targets with Iron sights and they elevlate. This can have signifigant effect on zero. Again high velocity and scopes it's not as obvious

I have a table of sights for all my match rifles with elevation and windage zeros for distance. Have looked at scopes that have mill dots for elevation. Used to have a varmit Unertil with two elevation cross hairs Idea was to bracket the varmit. Thing always confused me and caused misses, and am sure all those dots would do the same thing. Single Dot reticule, table of sights pasted to the stock, click in the settings for distance and windage is best for me.

Boats

Thank you, Boats, from the amount of experience you have I think your answer is most likely the one. Another BS award to Wikipedia- "23 inches of spindrift at 1000 yds for M193" ! Sounds like they had some wind!

[Chris]

You didn't tell us about your rifle (new, old, just mounted a new scope/barrel, etc..).

Make sure your scope is perpendicular to the rifle or you will get induced windage when making elevation corrections.

Here is a good article with an easy way to check.

http://www.longrangehunting.com/articles/r...ndicularity.php

Edited September 29, 2009 by Chris

[3GunF1Guy]

Order yourself Brian Litz's book and you will learn everything you need to know about spin drift. Including the math to figure it for youself and your gun. It will also give you real g1/g7 balistics on almost every bullet you could use.

Here is the link.

http://www.appliedballisticsllc.com/index_files/Book.htm

Scott

[ChristianHE]

You didn't tell us about your rifle (new, old, just mounted a new scope/barrel, etc..).

Make sure your scope is perpendicular to the rifle or you will get induced windage when making elevation corrections.

Here is a good article with an easy way to check.

http://www.longrangehunting.com/articles/r...ndicularity.php

Thanks Chris, that article is awesome! I will check using the technique given. No part of the rifle is newer than a year old and I have not modified or changed anything, I was just able to start about 6 months ago shooting at a range where I can go out to 600. So I've been experiencing new things...

I mounted the scope using a recommended technique of a plumb line and my rifle in my vise, padded and using paper shims to get it vertical using a bubble level that mounts to my rail, then lining up the vertical reticule with the plumb line. I have a feeling it is a little off.

Christian (also a "Chris" but not at your level... yet!)

[Mark K]

The Coriolis effect really only plays into really long hang time, like the 30+ seconds of high angle artillery. I was not an artilleryman, but I was an intelligence analyst of Soviet Artillery. The effect of the Coriolis Effect on a hang time if a second or two of a rifle or a tank round, is minimal and probably within the normal variation from round to round due to other factors (bullet weight, concentricity, powder and primer variations, etc).

Mark K.

[Boats]

Spin Drift is real and does apply to regular rifles. If you want a graphic illustration look at the Buffington Sight on a Trapdoor Springfield. It's calibrated to 3000 yards and has a real obvious cant to the aperture as the sight is elevated. 03's with the Arsenal sight same thing but it's less obvious for a high velocity round like the 30 1906. When you convert 03's to target rifles and install something like a Redfield or Lyman 48 you loose the compensation for the service rounds drift and have to click windage for increased distances.

I do think but don't know that spin drift is related to hang time more than the ballistic coefficient of the bullet. But that's from observation not any textbook or study. Hang time on a 500 gr 45/70 at 1000 yards is about 3 seconds. Long enough to shoot and see your strike through the spotting scope on a good day. The 1000 yard elevation setting on a Trapdoors Buffington has a clearly visible increase in windage from the 200 yard setting. This is not connected to the sights wind guage it's just cant to the elevation slide.

On your scope being plumb. It's a geometry question. To move point of impact 1 moa takes a very very small amount of twist. The distance your scope is off is probably going to require so little change to the rings it's not measurable. Better to keep a sight book with mechanical zeros out to the longest effective distance

Boats

Edited September 30, 2009 by Boats

[dt1]

Worrying about spin drift is kind of like feeling you need a titanium firing pin to reduce lock time. Lots of other things to spend your time being concerned with that are more important and will make you a better shooter

Where are you shooting out to 600yds around St. Augustine?

[Boats]

Theory is one thing actually shooting is another. From my Silhouette match book. 7mm 08 with 168 gr Serria Match kings I get about 1 moa of "spin drift" at 500 meters. In practice I don't compensated for it. Rams are 5 moa wide and in a match you get them presented left and right facing so the aiming point gets skewed relay to relay. The Ram is only 2 1/2 minutes high so elevation is what causes misses. If I was shooing bullseye at 500 with that rifle centering up my group would definitely gain points, more so at 600. Years ago when I shot a lot of over the course adjusted my mechanical zero when going prone at 600 nothing for the 200 & 300 yard legs.

However for game or I suppose snipers adjusting at mid range out to 600 for windage is generally not the right thing to do. Little bit off is not going to cause a miss fiddling with the windage dial often does cause misses. At most on days with steady 3 or 9 o/c wind I will add or take off 1 to 2 moa and 2 is a lot. Get a switch back and that 2 moa one way when the wind is the other makes a 4 moa miss. Thats 20 inches at 500. Long distance is another matter and windage much more important

Get the mechanical parts right then forget about them paying attention to breaking a good shot. Less you see in the scope the better. Dot and point of impact is all I look at.

Boats

Edited October 1, 2009 by Boats

[DUKE]

Worrying about spin drift is kind of like feeling you need a titanium firing pin to reduce lock time. Lots of other things to spend your time being concerned with that are more important and will make you a better shooter

Where are you shooting out to 600yds around St. Augustine?

+1 David. Shoot a 308 and learn to read the wind. I learn something new about the wind everytime I shoot from 800yds to a 1000 with a 308 very humbling.

[RufDog]

It should not be an upfront concern inside of 1000. It is real but If you are shooting a static 600yd line zero @ 6, same for a grand. Spend your time with reading wind. If you can shoot well enough to notice "spin drift" between yardages you are very accomplished.

[JohnRodriguez]

I don't even worry about spin-drift at 1000m. Im lucky enough that we have a 1000m range about 5 miles from where I live, so I do get to shoot it as often as I like. Your main concern sould be with making sure that your scope is level with the rifle. also, inslall a bubble level on the scope. You'll be amazed at how crooked the world realy is with a bubble level.

[Bronco]

I don't even worry about spin-drift at 1000m. Im lucky enough that we have a 1000m range about 5 miles from where I live, so I do get to shoot it as often as I like. Your main concern sould be with making sure that your scope is level with the rifle. also, inslall a bubble level on the scope. You'll be amazed at how crooked the world realy is with a bubble level.

Good advice, take it.

[askomiko]

Spin drift for regular 308 is around ~0.15mrad at 600m when zeroed at 200m, 0.3mrad for 800m, when the gun is zeroed at 300m. So, not much. You can zero the gun at a bit longer distance, say, 400m, so the spin drift becomes even less of a problem in medium distances. You'd be a bit left before 400m, dead on at 400m and bit to the right after that.

Of course, it makes a far less difference than the slightest breeze of wind, but it is one more thing to keep in mind for longer range shots.

I love installing scopes with a feeler gauge: just stick the gauge between the scope bottom and the base, assuming that both are flat of course. I guess that's very accurate method too.

Edited October 3, 2009 by askomiko

[Boats]

We can go on and on about spin drift and how important it is. Fact of the matter unless long range 500 and over on targets were precision is required it can be generally ignored. Smallbore prone with a .22 moving from 50 to 100 it is very important. Not much room for error.

Here is whats important to me though. I need to know my rifles "mechanical zero" that is what it will do if sights are centered windage and adjusted for proper elevation with that particular ammunition. Reason is when you shoot a sighter target and the strike is off when adjusted for mechanical zero you know what the ambient condition is doing to the strike. Might be a low strike on a cold day high one on a warm day or more likely a rifle range that does not have targets set exactly at the distance they are supposed to be. Strike will tell you how to manage your elevation settings. If you shoot a tight group at 600 all breaking centered and the group is 9 inches right all shots fired with the same observed condition you know there is 1 1/2 minutes of wind affecting the bullet. 1 1/2 is about the spin drift on .30 cals at 600 so if not cranking the sight for it before shooting you could be ticked into assuming there is 3 moa of wind.

Hathcock gained his skills on the target range. I bet he knew his drifts and distance zeros exactly.

Boats

[ChristianHE]

Thanks for all the info and opinions, I appreciate it. (even though some obviously did not read my thread-starting post!) I'm undecided on whether to remount my scope though. I'm definitely going to do the 100yd 15-20 MOA dial-up test suggested to see if my reticule is not "square", i'll update y'all next week! I want to make sure I'm still the weak part of the equation before Ft. Benning! (This time I have extra parts including a bolt.)

DT1 : I shoot 300 and 600 (and other distances in between when the others at the line agree or no one else is on the 600!) at Bradford Sportsman's Farm about 60 miles West of St. Aug, almost to Gainsville. bsfShootingSports.com Open WEd and Sat/Sun, $15-$20 or membership for $200 a year I think it was.

For me, my 6" groups of 5 at 600 using sandbags and with the Timney trigger are not an "accomplishment" anyone can do that... Now, if I had just run through and shot a pistol then shotgun parts of a stage so my heart was pounding and I was breathing hard, then did it without excellent support, then I'd be bragging!

[kgunz11]

Anybody telling you they are getting spin drift at 500 meters is either pulling your leg or watching too much Twilight Zone. The amount of spin drift at 500 meters with a modern rifle/caliber is immeasurable.

If you are progressively shooting farther and farther right incrementally in distances out to 600 yards you must likely have a canted scope or canted reticle. In the last 5 years I've fired over 20,000 rounds of .308 from 5' to 1400 yards, and I can give you a great big ole list of things that become important at distance that aren't up close.

First of all, you're not getting any spin drift at 600 yards. The Coriolis effect is not giving you any deviation that you could measure. We only start to see the effects out beyond 1200 yards and the caliber used has some control over the amount.

You'd be better served shooting and recording data than reading about extreme long range ballistics which a 6.5 Grendel is not capable of. And a point of interest, wind directions change through the year, and often daily. A North facing range is not always going to give you a 3-9 wind current.

[kgunz11]

And another tidbit of information from a former .22BR World Record holder...

-Shooting in a constant wind is better than no wind at all. Bullets do all kinds of swirly things when there's no wind.

-There is no better teaching tool than practice and time on the range.

-Burn out a barrel in a .308 and you'll still be in the infancy stages of reloading. Burn out too and you're beginning to learn how to shoot. (I'm on my 4th bbl and I only shoot less than 600 yards to do load development. Most of my range time is spent at 600 and beyond.)

[Boats]

Published data for the .30 cal 1906 give spin drift about 3/4 moa this from Hatcher. It's progressive over distance so way less important at shorter ranges. Thats why people don't worry about it under 600. 3/4 moa is pretty hard to figure from groups on paper at ranges less than 600 it gets lost in the other errors.

7mm08 Silouette rifle I account 1 1/2 moa change in zero at 500 to scope mounting more than anything else. For 385 Turkeys use the same 1 1/2 moa adjustment but they are skinny critters and need to have windage zeroed up good. Chickens @ 200 and Pigs @ 300 shoot it at zero. It's got 10 in a row pins for everything but Rams and my misses there are due to elevation not windage

That particular rifle has data covering sights and strikes for every shot fired since 1993 hundreds of club matches state matches and 3 national championships. Data books are better than any theorys every gun set up and shooter is different. Have not used my 03 match rifle much since I started shooting silouette but used to use 1 moa at 600 and 1000 Always set the Redfield at zero for 200 & 300

Your record book is going to tell you whats best for your particular set up. Not just windage but changes in elevation due to temp, different ranges component switches etc, Best thing a shooter can do is keep a record of strikes, you will learn faster and make fewer mistakes. You mentioned in your first post your shooter friend from Benning kept a dope book. Probaby no better recomandation for one than that.

Boats

Edited October 2, 2009 by Boats

[Jaxshooter]

KGunz that sounds like something Tim McWhorter would say.

[ChristianHE]

Anybody telling you they are getting spin drift at 500 meters is either pulling your leg or watching too much Twilight Zone. The amount of spin drift at 500 meters with a modern rifle/caliber is immeasurable.

If you are progressively shooting farther and farther right incrementally in distances out to 600 yards you must likely have a canted scope or canted reticle. In the last 5 years I've fired over 20,000 rounds of .308 from 5' to 1400 yards, and I can give you a great big ole list of things that become important at distance that aren't up close.

First of all, you're not getting any spin drift at 600 yards. The Coriolis effect is not giving you any deviation that you could measure. We only start to see the effects out beyond 1200 yards and the caliber used has some control over the amount.

You'd be better served shooting and recording data than reading about extreme long range ballistics which a 6.5 Grendel is not capable of. And a point of interest, wind directions change through the year, and often daily. A North facing range is not always going to give you a 3-9 wind current.

OK, thanks KGUNZ, that's the type of "for damn sure" talking from experience I was looking for! I've only shot about 2000 rounds out of my 6.5 Grendel and only 500 out of my new LR-308 that I put together, so yes sir I am just gettin' luke warm... Are you sure about the wind though, I read on Wikipedia that if you face North you always get a 3-9 wind No, I was just saying that everytime I've been to that range before that one windless day it was always a West to East breeze... Couple things I have learned from my rifle and scope: medium blue seems to be the easiest color for me to see at distance for me. (4x Nightforce NXS). The 300 range is perpendicular to the 600, so with the tail wind my hits were a bit higher than my ballistic calc dope said.

[kgunz11]

As for the ballistic calculated dope, this post could turn into a short novel. Unless your using a G7 drag function the chances your dope is correct are pretty slim. You'd also need solid MV from a known accurate chrono. Best advice for creating a dope chart is actual shooting in the field and recording the data.

I shoot a monthly 1000 yard match in Alabama with some intriguing wind conditions due to the terrain and tree line. In early Spring it is typically a strong northerly head or tail wind with a little left to right twitch to it. In late Spring it comes across the range diagonally, and by late summer it is almost horizontal across the range. I've seen it as light as 1-2mph and as strong as 30mph during match conditions. About 30 minutes East of that range I've shot in F-Class matches at Ft. Benning. The 600 yard range and the 1000 yard range there are less tricky in making wind calls.

The best advice I can offer anyone interested in long range shooting is to record data, lots of it. In order to do that you must shoot a lot. Temperature, humidity, and altitude play a big part in long range shooting. Learning to read the wind is something that comes from experience. It helps that I get to shoot along side this guy and benefit from his vast experience. http://www.whiddengunworks.net/accomplishments.html

[askomiko]

The best advice I can offer anyone interested in long range shooting is to record data, lots of it. In order to do that you must shoot a lot.

+2.

Calculations are getting pretty good nowadays, and you can save some range time with less guesswork. Here's an example of modern calculations, combined with a very skilled shooter of course.

Quick Target Unlimited (comes with QuickLoad) includes measured doppler data for some bullets, which means that the results are getting awfully close to real life. Actually, there's a free version on Lapua's site, it only includes Lapua bullets and works to ~1100m. http://www.lapua.com/index.php?id=1215

Here's a good book on the subject: http://www.appliedballisticsllc.com/index_files/Book.htm