Spin drift

[Augustus]

Re: Spin drift

Well well, there is hope in the world. Just a couple of short years ago many of the elitist on this site denied the existance of spin drift at distances encountered with shoulder fired weapons. They ridiculed anybody that suggested they were seeing the effects of such. I remember being told it was wind, canting of the rifle, poor shooting skills and quite possibly was caused from being born naked. Fixes such as curling the left corner of the mouth or the slight flexing of the little toe on the off side would alliviate the affliction.

At least now the discussion is not if spin-drift exists, but how much it affects a projectile and if correction should be dialed in. Yep, change comes hard and many of those who would be expected to lead is reduced to being dragged into the future. The history books are full of brilliant men resistng new ideas and technology. Many of the great minds resisted rifled barrels, repeating arms, and the use of aircraft for military purposes. Well anyway, no one can stop the march of progress. Those who have tried have been trampled underfoot by those with foresight. If I have to go one on one with a rifleman at extended ranges, I pray he is one that believes 1 moa is not worth messing with.

 

[lanwickum]

Re: Spin drift


I agree with the pulling the trigger thing. It is a more common "problem" than drift. I used to see my self doing it. Now I have to force it, I think. When I first started shooting I had 10" RH "drift" at 1000yards. I don't now. The wind today was very slight. 1mph or less. I was watching the smoke from the suppressor. Had to watch mirage as no grass would move.
I let a couple people shoot after me with my rifle. They both missed the first couple rnds holding center. They don't shoot precision rifle much. This was at 800yards.

Again, my opinion. It happens, it is slight. Within 1000, I don't pay much attention. That is why I held edge today with the slight L to R wind. I missed, at 800. Keep it as one of those things to remeber and not worry much about in the back of your mind.

 

[CCooper]

Re: Spin drift

Yeah

So what you are obviously saying is no wind dope and spin correct only, yeah? [/quote]

 

[Graham]

Re: Spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Augustus</div><div class="ubbcode-body"> Well well, there is hope in the world. Just a couple of short years ago many of the elitist on this site denied the existance of spin drift at distances encountered with shoulder fired weapons. They ridiculed anybody that suggested they were seeing the effects of such.</div></div>Nobody ever said that spin drift doesn't exist. But many did say that they have seen it used as an explanation of covenience by instructors who were otherwise unable to analyze poor technique. As Bryan says:<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">To put the spin drift magnitude into perspective, most rounds will see something like 5" to 9" of SD at 1k. Now consider that the bullet will be displaced laterally by about 5" for every 1 degree of rifle cant. Without a level, shooting in the field without a vertical or horizontal reference for your reticle, a typical shooter would be lucky to achieve less than 3 or 5 degrees of cant. The average bias of cant would probably be affected by being left handed vs right handed; hence LL's observation of the left handed shooter using much different wind than the right handed shooter...a horizontal drift on the order of 5" to 8" can be seen repeatably in calm conditions. Of course if the wind is a big deal, the spin drift is less significant by comparison, but it's still there.</div></div>So, the question is not whether spin drift exists, but whether it matters as a factor given the conditions and other more significant variables present at the time.

I myself have seen a military instructor tell his class that there's 1.5 MOA of spin drift at 1000 yards. He was simply repeating what he had heard: when I asked him whether he routinely dials 1.5 MOA at 1000 yards on a calm day he admitted that he doesn't.

 

[DaveV]

Re: Spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Augustus</div><div class="ubbcode-body"> Well well, there is hope in the world. Just a couple of short years ago many of the elitist on this site denied the existance of spin drift at distances encountered with shoulder fired weapons. They ridiculed anybody that suggested they were seeing the effects of such. I remember being told it was wind, canting of the rifle, poor shooting skills and quite possibly was caused from being born naked. Fixes such as curling the left corner of the mouth or the slight flexing of the little toe on the off side would alliviate the affliction.

At least now the discussion is not if spin-drift exists, but how much it affects a projectile and if correction should be dialed in. Yep, change comes hard and many of those who would be expected to lead is reduced to being dragged into the future. The history books are full of brilliant men resistng new ideas and technology. Many of the great minds resisted rifled barrels, repeating arms, and the use of aircraft for military purposes. Well anyway, no one can stop the march of progress. Those who have tried have been trampled underfoot by those with foresight. If I have to go one on one with a rifleman at extended ranges, I pray he is one that believes 1 moa is not worth messing with. </div></div>

So <span style="text-decoration: underline">you</span> do or don't dial for SD?

 

[Augustus]

Re: Spin drift

Yes, I hold for spin drift.

 

[Kenny_Wasserburger]

Re: Spin drift

Have read this thread with a good deal of interest.

IN our long range game with Black Powder and cartridge rifles, (I shoot a 45-110 Sharps) we do have spin drift issues to contend with.

The old timers even knew of it, look at the buffington Sight on a Trapdoor Springfield it has the drift compensated in the staff.

Many of us zero at 200, yards with 2.5 to 3d MOA left on our scopes or Sights thats about what the drift is at 1000 yards. Quite a bit for our old heavy 500+ grain bullets, at one mile it is on order of 8-9 MOA.

Kenny Wasserburger

 

[Noel Carlson]

Re: Spin drift

Welcome Kenny,

I did not know that the Springfield built SD compensation into the sight, but it makes alot of sense. Forty-two years later, the rear sight of the stockable "Artillery Luger" P-08 was also designed to automatically compensate for SD, in a 9.8" twist, at roughly 2,000 fps MV.

 

[zenbiker]

Re: Spin drift

The question I've always had about spin drift is in the explanation that the bullet is spinning and the ridges of the engraved rifling are supposedly engaging the air as the bullet passes through the fluid medium. The thing is, if that is the case, the bullet should be enganging the air all around its surface; so why does it drift <span style="font-style: italic">right</span>? It not as if this is a sinker or curve in baseball where the ball spins on an axis oblique to the downrange vector, unless the bullet is not pointing straight downrange during flight, i.e. precessing, and tending to present the bullet axis at an angle to the right of the flight path. If such was the case, spin drift would vary with the actual precessional yaw of the projectile, determined by rotational velocity, muzzle velocity, barrel twist, and quality of the barrel crown.

Which, like Lowlight said, is a good reason to rely on range data for your particular rifle/ammo combination than a set figure.

 

[Lindy]

Re: Spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If such was the case, spin drift would vary with the actual precessional yaw of the projectile, determined by rotational velocity, muzzle velocity, barrel twist, and quality of the barrel crown.</div></div>

Well, it does. It's just that it's difficult to compute the effect of those things, and most programs don't try - they just produce an estimate.

See:

http://exteriorballistics.com/ebexplained/5th/42.cfm

As well as other explanations in:

http://exteriorballistics.com/ebexplained/index.cfm

 

[Greg Langelius *]

Re: Spin drift

Building on this, I honestly doubt I am a sufficiently adept marksman that I can shoot with the precision and consistency necessary to allow spin drift to emerge as a significant issue. It's really a comparatively miniscule segment of my concerns. I suspect that with few exceptions, most of us cannot shoot well enough to demonstrate either the presence of absence of spin drift on a reliable basis.

Greg

 

[zenbiker]

Re: Spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">Building on this, I honestly doubt I am a sufficiently adept marksman that I can shoot with the precision and consistency necessary to allow spin drift to emerge as a significant issue. It's really a comparatively miniscule segment of my concerns. I suspect that with few exceptions, most of us cannot shoot well enough to demonstrate either the presence of absence of spin drift on a reliable basis.

Greg </div></div>

Yeah, what he said. I got other things that concern me more when it comes to hitting the target.

 

[Guest]

Re: Spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Wadcutter</div><div class="ubbcode-body">I live in Australia, so any spin drift from a right hand twist barrel is reduced a bit by the influence of the Coriolis effect.
So I wonder why in the U.S. left hand twist barrels are not more popular for long range rifles? Seems like you could reduce the effect of spin drift at no cost. </div></div>

This is an off topic answer but here goes anyway.

Many years ago I was heavy into drag racing, an doing well. My friend was into turning left only. One night while dyno testing an engine I had built for the left turner's, I ask why they never ran a left hand rotation engine? I got the deer in the headlight look. Long story short, built a lefty for them, change the Diff around, reweighted the car and cleaned up the first race. Was protested torn down, and kept the win. Seems there was nothing in the rule book about which way the engine had to turn,...until after that Saturday night was in the books. The US Military found out during WW I an WWII South of the Equator they had less trouble with left hand rotation engines vs right hand, but north the right hands ruled.

Now Back to the shortest spin drift, thread I seen on this board,...ever.

As I said before, I prefer a canted retical (yes, I have levels on both sticks) over dialing for S/D as I don't want to spend any time crunching more numbers than I have to. I don't know were SR or LR ends let alone where ELR starts, but I do know where they all are for me.

 

[DTubb]

Re: Spin drift

Across the Course and long range shooters are able to discern spin drift from an iron sighted match rifle (with sights properly levelled).
One of the aids I use when teaching is an 1898 30/40 Krag. Flip up the rear sight (220gr round nose at approx. 2300fps). Precession is already present in the rear sight.

If really want to see how stark a contrast it actually is.
Take your leveled rifle with it's 1000 yd elevation and windage zero and go to the 1000 inch range (most will not of heard of a zeroing range quite this short).
Hold at an aiming mark at the bottom of a vertical line (3 ft tall vertical line will be sufficient) and watch where your (windage) impacts print. You will need a plumbob in order to assure you have a true vertical line.
dtubb

 

[Mag 300]

Re: Spin drift

Thanks for the info
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DTubb</div><div class="ubbcode-body">Across the Course and long range shooters are able to discern spin drift from an iron sighted match rifle (with sights properly levelled).
One of the aids I use when teaching is an 1898 30/40 Krag. Flip up the rear sight (220gr round nose at approx. 2300fps). Precession is already present in the rear sight.

If really want to see how stark a contrast it actually is.
Take your leveled rifle with it's 1000 yd elevation and windage zero and go to the 1000 inch range (most will not of heard of a zeroing range quite this short).
Hold at an aiming mark at the bottom of a vertical line (3 ft tall vertical line will be sufficient) and watch where your (windage) impacts print. You will need a plumbob in order to assure you have a true vertical line.
dtubb </div></div>

 

[wadcutter]

Re: Spin drift

I have been shooting out to 2285 yards a number of times, over the last week or so and yes I have calculated drift prior to the shot.
I did however not dial in any windage correction prior to the first shot/shots as I wanted to see where the first bullet or three landed.
This was going to be a check on my wind reading skills and also to see if I could actually sucessfully calc drift.

The answer is no. I was from 1.5 to 4 MOA out in my worked out windage due to the variables in the wind speed and direction.

At long range wind is not constant over the whole distance, and a perfect still day is rare.
I hope to get a perfect day soon, but I am still waiting.

A greater issue was getting the bullet to the target without it being unstable from its passage through the transonic barrier. 1 out of 3 hit the dirt way low.

 

[Kenny_Wasserburger]

Re: Spin drift

David,

I just wanted to say how much I enjoyed our Brief go at the 1123 yard Buffalo at Raton last July. It was a real honor for me to adjust the sights and spot you on your shot. And again your stoping by my camper the next morning to say Hello. If you ever get Wyoming Way, your welcome at our Ranch for a go on our Steel Creedmoor targets with my old Sharps.

Kenny Wasserburger

 

[john_1182]

Re: Spin drift

Hi all, i dont often poke my head up around here but i find the question of "should i caculate for spin drift?" a interesting one.

i totaly understand that there are sooooooo many other variables that come into play and can mask variances to any shot (cant/ wind/ standerd deviations/ trigger pull/ ect). i havent been caculating for SD but i will be ,i have just bought a apple i touch with the sole reason for it to use Knights Armament's "bullet Flight" app for my long range shooting and it caculates for SD and coriolis effect (i dont bother with CE at the moment because where i shoot it is giving me less then .125 MOA effect) (caculated by bullet flight)

im personaly of the opinion that why not correct for SD if it can be caculated for correctly, i look at it in the same light as caculating for wind, its there so why not correct for it

P.S. here is a quick list of SD corrections bullet flights gives me

.308
165gr sierra game king
45gr varget
lapua brass
cci primer
seated just of the lands
2650fps
BC1 G1 .397
BC2 G1 .402 2400fps
BC3 G1 .411 1597fps

200y .1 MOA of SD
400y .2 MOA of SD
600y .4 MOA of SD
800y .7 MOA of SD
1000y 1 MOA of SD

even if i am not fully capiable of producing the perfect shot every time i sill think worth its caculating for as you can see from the data above. (heck it even gives me .4 MOA SD for my .22cal at 150 yards)

 

[Lindy]

Re: Spin drift

The data you displayed are (1) almost certainly incorrect, as most loads at 1000 yard are closer to 1 MOA of spin drift than 0.1, and (b) not calculated.

You cannot calculate spin-drift without a 6 Degree of Freedom program and a lot more information about the bullet and conditions than the program has.

For more information, see:

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

and

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

 

[john_1182]

Re: Spin drift

thank you for the correction,

A) the .1 MOA @ 1000 was a typing error on my behalf, and for the links, its always to have a bit more detailed info

B) as far as i know the SD is caculated fairly correctly, (i only assume so for all of what i have read online about guys and gals in the US military using this app to help with there long range caculations

so, ok yes i am fully aware that to caculate the true spin drift requires alot more information i was displaying SOME of the information inputed into the app just to display what i had found. (couldnt be stuffed typing up tings like angel of fire, air pressure, temp, ect)

here is a link to what the app, its easier to link to the app then try and type it all up (first pic is shooting conditions, selected round and what to dial, 3rd pic is the full info about the round), (of course the data i put in my last post was for my particular round, sorry for going way off topic, but im just trying to show how i come up with my SD values)

http://www.knightarmco.com/bulletflight/index.htm

 

[Lindy]

Re: Spin drift

I know the web page says it computes spin drift. I have some appreciation for the computational complexity it takes to do that.

Bryan Litz says in his book,

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">A 6 Degree of Freedom (6 DOF) computer program, combined with aerodynamic prediction software, is capable of modeling all of the dynamics that cause spin drift and other complex effects. The 6 DOF program is too complicated for general use, but it is possible to run the program for a set of representative bullets and study the level of spin drift for each. It's then possible to key in on the most important variables related to the spin drift and produce a predictive equation that can be used to characterize the effects of spin drift rather than calculate it directly.</div></div>

I suspect that is what the program is doing. That's not a problem - the test of a computer model is whether it produces useful predictions - but it's not the same thing as directly calculating spin drift. The equation Bryan uses in his program(s) for doing that is in his book.

Heck, I have a simplified model for wind drift which I use very effectively in the field, which neglects barometric pressure and temperature, but still produces useful predictions for field shooting.

It just sets off my B.S. alarm when claims are made that are almost certainly not true.

 

[BryanLitz]

Re: Spin drift

BulletFlight does use my spin drift equation.

Although it's true that the equation isn't directly calculating spin drift, it's easy to understand how a user can perceive the output as a 'calculation'.

I don't think John was trying to be misleading by sharing the 'results' of his program weather they be calculations, predictions, approximations, etc...

-Bryan

 

[Lindy]

Re: Spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">BulletFlight does use my spin drift equation.</div></div>

Excellent! I'm glad to see authors of ballistic programs using your work!

It's not a problem - John and I swapped P.M.s on it, and he clearly understood my point.

Added comment: I started messing around with ballistics programs a decade or so ago. At that time, the few that were available were expensive, limited, and ran on few platforms.

No one but aircraft pilots had ever heard of the concept of density altitude.

Today some of the really good programs are free, available to anyone with a computer linked to the Internet, and the number of handheld platforms is increasing. You can haul a rugged handheld platform into the field, or be quite accurate with a firing table based on density altitude and some simple measurement tools.

Life is good.

 

[josephberry]

Re: Spin drift

Lowlight, never considered the right hand, left hand factor. I'm a lefty and always seem to dial less SD than the right handers.

 

[WRM]

Re: Spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jdberry</div><div class="ubbcode-body">Lowlight, never considered the right hand, left hand factor. I'm a lefty and always seem to dial less SD than the right handers. </div></div>

He's not talking about which side of the gun the shooter is on....

Cheers,

Bill

 

[josephberry]

Re: Spin drift

No, but he is talking about shooter error at long ranges. Did you not read the part about the left handed shooter dialing in the least amount of windage?

 

[Lowlight]

Re: Spin drift

Talking about shooter error, again, on the line yesterday with a PR1&2 class...

One shooter with a rifle that needed 10.8 Mils to reach a 1000 yards using a 175gr BHA needed 2.5 Mils under current conditions, another shooter, on the same line, needed 1.5 mils, he was also left handed but other shooters on the same rifle used the same dope and hit equally well. The 1.5 Mil rifle, an 18" 308 that needed about 12 Mils to 1000 yards. My 16" AR10 needed 11.6 mils to 1000 yards and I held edge of plate... all during the same session.

The spread among 308s at a 1000 yards was varied and deep, the winds were switching bad, but the prevailing wind was about 7 MPH coming from the 75 degree direction.

So, now that I pay even more attention on the line, I am seeing roughly a 2 Mil difference in wind adjustments between 10+ shooters, that is 2 Mils at the shooter and not adjusted spread downrange. So we're talking an over an 75" spread because of technique alone.

 

[Lindy]

Re: Spin drift

How was the guy shooting the 168 SMKs doing at 1000?

 

[Lowlight]

Re: Spin drift

They wouldn't work at all, 2 of them couldn't reach 1000, and the other two were just falling out of the sky, my 16" AR10 with M118LR was doing much better.

Bad week for 168s to 1000.