Spin Drift

[THEIS]

Hi,

Now we get into the real conversation of jackets vs internal alloys

This has been talked about for a few years now..even to the point of utilizing bi-metal solids and pros/cons of that.

I think there are a couple different "reasons" we see jackets get blamed for "issues" instead of internal alloys:
1. It is EASY and HISTORICAL to just blame the jacket.
2. The jacket is something that the end user can put their hands on to feel and their eyes on to see.

I think the reason you do not see more people talk about improving the internal alloys are:
1. For some crazy reason everyone seems to think that putting a harder, more dense alloy is going to upset the BATFE and make them criminals with "AP" ammunition manufacturing.
2. The potential issue for the jacket and the harder, more dense alloy "spinning" at different rates due to different weights. This has even been proven with lead cores.

I think in very near future we will see bi-metal solids that are copper exterior and tungsten or tungsten/copper interior. This will allow the projectiles to have the length of standard jacketed projectiles but the density and weight of the super long solids that nobody can get to stabilize
Higher sectional density, higher BC, hyper-stabilization twist rate with smaller projectile footprint is a win win win.....

Sincerely,
Theis

 

[Greg Langelius *]

One metal that might work for a bimetal core is Bismuth. A core made from tin-sintered bismuth powder/granules (it is a beatch to cast as a solid slug; among other things, it expands as it solidifies, and has a brittle consistency.) might be a real dinger. It has a slightly lower (86%) density than lead.

Bismuth has unusually low toxicity for a heavy metal. As the toxicity of lead has become more apparent in recent years, there is an increasing use of bismuth alloys (presently about a third of bismuth production) as a replacement for lead.

- Wikipedia

Bismuth was long considered the element with the highest atomic mass that is stable. However, in 2003 it was discovered to be extremely weakly radioactive: its only primordial isotope, bismuth-209, decays via alpha decay with a half-life more than a billion times the estimated age of the universe

- Wikipedia

I once got hold of some granulated bismuth and used it for ballast in my Grandkids' Pinewood Derby Cars. The Boy Scouts had banned the use of lead for ballast. G&^$^&*D Snowflakes!

Greg

 

[Greg Langelius *]

Ode to Frank (aka "The Littlest Goombah")

Bryan fingered 10 fucking fairies,
Spinning right and free.
Jimbo fingered 8 fucking fairies,
But Frank only fingered 3.

"Spin those fuckers left!" Frank said,
"Spin them left and see,
There'll be no fucking fairies left
For fucking you and me"

I totally love the poem, gonna use it on the podcast

...Oh, no; dear God, Jim, not the poem...

ROFLMAO!

Greg

 

[Jim Boatright]

So, according to your statement, lead core jacketed bullets exhibit a spin drift trajectory that is 2-2.4% of the drop.

Dividing that into five .1% increments coincides pretty well with the five BC clusters (.400 - .800 BC ) found in long range lead core bullets.

So would it be wrong to line it up like this:
.800+ BC= 2%
.700+ BC= 2.1%
.600+ BC= 2.2%
.500+ BC= 2.3%
.400+ BC= 2.4%

Please do not take those ill-advised generalizations which I made from a very small 30-caliber data set as gospel. All of this is likely to change when we look at initially hyper-stabilized bullets launched at very high velocities anyway. Hyper-stability had not been thought of when that paper was published. I suspect that initial gyroscopic stabilities around 3.0 will show greater Spin-Drift at all ranges. Wait and see.

 

[Deleted member 113831]

Please do not take those ill-advised generalizations which I made from a very small 30-caliber data set as gospel. All of this is likely to change when we look at initially hyper-stabilized bullets launched at very high velocities anyway. Hyper-stability had not been thought of when that paper was published. I suspect that initial gyroscopic stabilities around 3.0 will show greater Spin-Drift at all ranges. Wait and see.

At the moment, I'm just trying to understand trends with lead core bullets spun at 25 to 30 calibers per turn.

 

[Jim Boatright]

At the moment, I'm just trying to understand trends with lead core bullets spun at 25 to 30 calibers per turn.

On the other hand, I am most interested in how today's best monolithic ELR bullets can be made to behave best at extreme ranges. I view application of new theory to old bullet designs as a necessary and desirable type of "backward compatibility." We have already learned what we can from them, and it is time to move on with better bullet designs, better rifles, and better software.

 

[Jim Boatright]

Okay so if it's a fraction of 2% based on the drop, let's look at this,

130gr Prime Ammo at 2800fps

8.0 Mils or 27 MOA to reach 1000 yard target

We'll figure 2.2% for a .585 BC

So I get

.176 Mils
.59 MOA
6.0 Inches

Yet my AB Calculator gives me .21 Mils or 7.2 Inches of drift, which is close but still more by a fair percent because the numbers are small. It appears if you round it up, you have an issue, you round it down, it's more so inline. 5" of drift vs 7.2", still not really a miss on target when you consider the wind.

My biggest issue is the solids are 1/2 of jacketed bullets giving weight to the idea that it's a combination of factors like jacket thickness along with the lead underneath. I have been told that this along with the twist rate can affect the bullet shape under the jacket. Are we getting shotty data because there is a potential to deform the core so a segment of the data is actually corrupt, leading to larger numbers?

If the jacket is such a wildcard, why has it not been addressed? A different core, thicker jacket, etc would knock these numbers down.

Because look what a solid does,

A Warner Tool Flatline based on my data means,

1000 yards is 6 MILs of adjustment with a 122gr 6.5

1.2% of 6 Mils to reach 1000 yard target is .072, or .25 MOA

It's more in line with my real-world results across the board. If Bullet has a thicker jacket and the twist rate is not disturbing the lead core the same way, you can easily have a lower number than 2% it can be 1.75% and have a measurable difference.

Funny solids are less than 3" (See Ode to Frank) and jackets are 6 to 7.2" under similar conditions, tells me it's inside the bullet not outside. The rifling is not going to really engrave the solid less, it's still copper, what moves is the lead core, which changes the flight characteristics and balances of which could add wobble. If you actually run the 2% vs 1.2% numbers it's huge.

2 Mils difference in bullet drop got you 1/2 the SD, seems pretty big. Why would you shoot a jacketed bullet or better, why would you continue to design a jacketed bullet if the results were so stark? Don't get me wrong I have been a solid fan for years and I have a long history with solids. These numbers alone would make jackets obsolete. At least it would change jacket technology or even better core tech, a stronger core would act like a solid because lead is so soft, a true target bullet could easily replace lead with something else.

I looked up densities of lead vs copper,

View attachment 6898658
They have a lead replacement designed just for this,

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Technon® offers many advantages to compounders:

Technon® has a spheroidal grain structure. This makes for a faster and better mix
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Ammunition: Projectiles and shots,

I am willing to bet if 2% can swing in small percentages up, it can also swing down with modern bullets and repeating the same value for something that is changing constantly like bullet design and manufacturing, it's not as big as advertised.

Please stop trying to generalize about spin-drift from a few worked examples. The next thing will be that somebody will notice that all jacketed, lead-core bullets are fired in 30-caliber rifles. I will add some hyper-stabilized examples in the next release.

The spin-drift is caused by aerodynamic lift force due to the horizontal yaw-of-repose attitude bias of the spin-stabilized bullet in flat-firing. For a RH spinning bullet, the rightward yaw-of-repose angle is the accumulated effect of rightward torque impulses occurring twice per coning cycle as the trajectory arcs downward due to gravity. The ratio of spin-drift to drop from the bore axis rapidly approaches an invariant fraction as a limit beyond 150 yards, or so. That fraction can be evaluated when the bullet has slowed to an airspeed of Mach 1.2 as the ratio of that bullet's horizontal lift force attributable to its yaw-of-repose to the constant weight of that bullet. I explained why this simple evaluation is just as good as running a 6-DoF flight simulator in the spin-drift paper. The estimated spin-drift matched PRODAS results within about 0.2 percent for the M118LR Special Ball 7.62 military ammunition. The results might have been better if I had the details of that military bullet shape. The Army originally told me those PRODAS runs were for the 175-gr SMK bullet, but they clearly are not. If anyone has a dimensioned drawing of that 172.16-gr military bullet, I would appreciate seeing it.

Jim Boatright

 

[Deleted member 113831]

I don't think you understand what is going on here Jim...We aren't taking your numbers as gospel. What you have opened our eyes to, is that SD is some percentage of drop.

If that percentage is more or less constant for any specific rifle / bullet combination, then that number can be discovered and calculated by the user. We don't have to rely on lines of someone's code in some ballistic program to do it for us.

I can't do calculus, and even if I could, I wouldn't be doing it on the firing point. But a simple percentage? Well hell, I can do that with a $5 calculator or a pencil and paper if I have to.

That is what are talking about.

 

[damoncali]

Spin drift is not a percentage of drop. You may find that to be true as a rough rule of thumb in some cases, but that's not an improvement over Miller-like simplifications used by some ballistics calculators. You can only dumb it down so much, and percentage of drop is a step too far.

 

[Deleted member 113831]

Spin drift is not a percentage of drop. You may find that to be true as a rough rule of thumb in some cases, but that's not an improvement over Miller-like simplifications used by some ballistics calculators. You can only dumb it down so much, and percentage of drop is a step too far.

So, in a specific rifle / bullet / load combination, what are the factors that affect the variables of spin drift, that woudn't also proportionally affect drop?

I get that you can't put out a specific number for a caliber, or a bullet, or a rifle. But for a single specific rifle / bullet / load combination, exactly why does that not work? We aren't looking for answers to the third decimal place. If a rule of thumb can get us +/- 10% then that is only +/- an inch difference or less at 1000 yards. I can live with that.

 

[Lowlight]

I think the numbers are more realistic by using a small percentage of the drop, they match closer to real-world observations.

It was the 173gr Special Ball they used, super crappy bullet, it's like a 168gr SMK more than a 175. And it was going 2500fps out of a 30-06 so it may match the current M118LR in your program but none of the data matches in the real world. It's wrong by a wide margin, honestly, if you're gonna default to simulated again, who cares, we can make any level of simulation match a pre-determined outcome. Everytime an actual test is tried it's much smaller than the simulation by a measurable amount. As it is, the AB39 stuff is a different MV than the M118 stuff so things change all the time. Now special ball from the 70s is the exact match of M118.

I shot the special ball in the USMC, it's not good, in fact, my Hog's Tooth is a once fired special ball round, I have the shot dimensions, but funny to see if they are square, lol.

Taking your drop from your rifle and not overlaying the flat rate value on it is closer to reality. The data from the papers here have 8" to 12" but the real world value in the same paper is 6" so which is it ? 12, 8, or 6

 

[damoncali]

So, in a specific rifle / bullet / load combination, what are the factors that affect the variables of spin drift, that woudn't also proportionally affect drop?

I get that you can't put out a specific number for a caliber, or a bullet, or a rifle. But for a single specific rifle / bullet / load combination, exactly why does that not work? We aren't looking for answers to the third decimal place. If a rule of thumb can get us +/- 10% then that is only +/- an inch difference or less at 1000 yards. I can live with that.

I'm just saying your chucking an approximate calculation and replacing it with a rule of thumb that is basically a simple curve fit through your DOPE. If you've got DOPE, you don't need a calculation in the first place. The value of calculation is that it's a substitute for DOPE - what you do when you don't yet have real data. If you've got data, just use it. If not, use the best calculation you can.

I also question the ability of the average shooter to be able to measure spin drift on a typical range. It's not easy to tease out with any precision. But that's another issue.

To answer your question, though, drift is caused by yaw induced lift. Yaw impacts drag, lift, and the tendency to yaw even more. Drop is primarily a drag thing. Yaw impacts drag, which impacts drop, but not in the same way it impacts lift. It's all related, but there's no simple relationship between lift and drag.

 

[canezach]

Maybe I'm not reading enough into it, and I understand the 2+2=4 analogy, but if a simple 1 MPH error in your wind call compared to actual wind value, which most people would say is pretty damn good, can push your projectile 6" or more at 1K, when do I get to blame spin drift for my mistake in judging the wind?

 

[damoncali]

Maybe I'm not reading enough into it, and I understand the 2+2=4 analogy, but if a simple 1 MPH error in your wind call compared to actual wind value, which most people would say is pretty damn good, can push your projectile 6" or more at 1K, when do I get to blame spin drift for my mistake in judging the wind?

It's only useful for first round hits. If you miss your shot by less than the spin drift and didn't account for it, you can blame spin drift. (If your hold was perfect).

 

[Lowlight]

A 1 MPH wind blows at 175SMK 10" at 1000 yards, which just happens to be what they say is the SD at 1000 yards for the same bullet, go figure.

They model it, hence the PRODAS comments, they don't have a real measurement for most of this stuff we shoot today. They are extrapolating other data.

In fact, if you take Damoncali post above, if it's a YAW Thing and most software is 3 DOF how the heck are they figuring it when 3DOF does not include Yaw like 4DOF and 6DOF try to do. The question we are exploring is where is the number from like Hornady went to Spark Data range and their numbers are 3" less at 1000 yards (on average) so each time they try to figure it out today, it's shrinking, which is part of my point.

 

[damoncali]

You could argue it's never worth worrying about because at ranges that it really matters, you're going to need DOPE to have a realistic chance at a first round hit. Taking a cold rifle to a new location, calculating a trajectory at a mile, and hitting it with no previous DOPE on the first shot is going to be almost a fluke unless the target is huge. And if you have DOPE, spin drift is already rolled into it.

But yeah, the way most calculators deal with it is with a similar technique to the Miller stability rule. It's surprisingly good (to me, at least) given how little information is used, but it's not perfect by a long shot. The only alternative to improving that is really to get more detailed bullet information. You can calculate lift and overturning moments with some degree of accuracy (and use them in an MPM, for example), but even that's not great. You can measure it on a spark range, but that's really expensive. Bottom line is that it's hard to pin down as precisely as we're wanting it to be.

 

[Lowlight]

That is all changing which is why Jim is chasing Solids at ELR Distances

The ELR World Record stuff has them getting 1st round hits to at least 2500 yards now, you cannot keep falling back on what we used to do. Sure a lot of people cannot shoot past 1000 yards, but a lot more can. Time to change the dynamic

 

[canezach]

It's only useful for first round hits. If you miss your shot by less than the spin drift and didn't account for it, you can blame spin drift. (If your hold was perfect).

When you said "if your hold was perfect", that's the point I was facetiously making, though the joke was poorly made. I know what spin drift is and I'm not disputing its effect, but there are so many potential errors from just the shooter (bad body position/recoil management, sloppy trigger discipline, misjudged wind, etc) that I would likely blame myself for a hundred different things before I thought of spin drift

 

[Lowlight]

I feel the same way, it's more likely a wind call error or shooter error (Shooter Drift) before it was SD... however, and this is big,

we are shooting smaller targets that according to the numbers would be a Miss, and most of the time it is not a miss. It's a hit, so either we are blowing the wind calls in our favor, or blowing the trigger press in our favor or a combination of things, to include, in my mind the fact, the data being used is wrong, and the value for the Spindrift offset is much smaller than being advertised.

Sure can make mistakes in our favor, but the numbers don't support the real world results, has always been my point.

When I shoot a 1 round per target match and score a 56 out of 60, not using it, you have a data problem.

 

[damoncali]

It all depends on how small a target you want to hit... Personally, I don't get the fun in trying to hit a 10 foot square target super far away. That's artillery, not marksmanship. If you want to hit something smaller, you're going to need to get this stuff right (as right as you can), or use some spotters (which are kind of a downer). It's not optional (or even negligible) like it is at sane ranges. Your hold and wind call have to be perfect too. Neither of those is optional either. Things like the flat earth assumption begin to enter your mind at 3000 yards.

I don't personally have strong opinions on exactly how big spin drift is for any given bullet well into the trans/subsonic range, because I'm sure I can't tell from behind a rifle. I can tell you how big it is in theory, which is based on assumptions backed by imperfect data, but that and a spotter will get you close. We're talking about stuff that's pushing the limits of predictive calculation of any kind. Maybe the CFD-RBD stuff can do it. That's some highspeedery I'm not up to date on.

 

[LastShot300]

I still don't get how a shooter can isolate SD from wind, canting, etc...and make claims about its real world influence on the calls, and I still wonder if even a spark range can really put a real number on it. That's the reason Yaw Cards were invented in first place AFAIK.

 

[damoncali]

I have no idea how people can see it at the range. I can't even come close. But a spark range can tease out overturning moment and lift coefficients with good accuracy, and then you can get a pretty good calculation from MPM or 6DOF.

Yaw cards predate spark ranges, which are significantly more accurate (and costly). McCoy puts the origin of yaw cards with Mann in 1909, but I kind of doubt he was the first - it's a fairly obvious thing to try. But he definitely documented them. If you haven't read Mann's book, treat yourself and do so. It's a fantastic piece of ballistics history. Details here on spark range vs yaw cards:

http://citeseerx.ist.psu.edu/viewdo...9FB8DF?doi=10.1.1.1000.3805&rep=rep1&type=pdf

 

[LastShot300]

I have no idea how people can see it at the range. I can't even come close. But a spark range can tease out overturning moment and lift coefficients with good accuracy, and then you can get a pretty good calculation from MPM or 6DOF.

Yaw cards predate spark ranges, which are significantly more accurate (and costly). McCoy puts the origin of yaw cards with Mann in 1909, but I kind of doubt he was the first - it's a fairly obvious thing to try. But he definitely documented them. If you haven't read Mann's book, treat yourself and do so. It's a fantastic piece of ballistics history. Details here on spark range vs yaw cards:

http://citeseerx.ist.psu.edu/viewdo...9FB8DF?doi=10.1.1.1000.3805&rep=rep1&type=pdf

My point exactly, Spark Range is not good enough though fine for calcs. I have read Mann so thanks.

 

[sandwarrior]

On the other hand, I am most interested in how today's best monolithic ELR bullets can be made to behave best at extreme ranges. I view application of new theory to old bullet designs as a necessary and desirable type of "backward compatibility." We have already learned what we can from them, and it is time to move on with better bullet designs, better rifles, and better software.

That's a good question, Jim. I have to wonder how beneficial it is to use a lighter bullet that is longer and sleeker than a jacketed bullet. But, where does weight come back into play? Maybe a monolithic bullet of an alloy that helps add weight? Maybe construct a monolithic bullet like a hollow point where you can put the CG rearward, or even forward?

I mean, I understand the lighter, longer monolithic bullets are working. I just wonder if there were factors we could introduce back into them that give advantages of the jacketed bullets without having the concentricity issues. Just thoughts in the wind.

 

[Jim Boatright]

Let me say a few words in defense of PRODAS and other 6-DoF flight simulators. These are the most sophisticated trajectory propagations available. They integrate the Equations of Motion for a projectile in very small time-steps using sophisticated numerical techniques which have long been used in aerospace applications and which minimize the accumulation of computational noise. Linear aeroballistic theory and the physical laws of dynamic motion are built into the EoM. The initial launch conditions are specified by the user for each simulation run., including the environmental factors. The mass properties and aeroballistic coefficients of the projectile are specified interactively by the user by running a pre-processing program. The decay of the initial spin-rate of the projectile is calculated for each time-step from pre-stored spin-damping coefficients which are Mach-speed dependent. It is nearly exponential in flight time, but not exactly. The 3-dimensional air-flow approaching the bullet is calculated for each time-step, including expected changes in air density, temperature and winds at that location of the projectile in its trajectory. The direction of the spin-axis is updated based on the overturning moment calculated aerodynamically from pre-stored mass properties and Mach-dependent coefficients and the current spin-rate of the projectile. The lift and drag forces acting upon the projectile are calculated for each time-step based on pre-stored Mach-dependent coefficients and the attitude of the projectile relative to the approaching airstream. By using small enough time-steps, complicated relationships become linear in accordance with the physical laws of conservation of linear and angular momentum. Each data reporting interval spans many computational time-steps.

PRODAS, for example, knows nothing of Coning Theory, yet its computed trajectories demonstrate it. It certainly does not rely upon any of the many analytically generated trajectory shapes which have been attempted over the centuries. It knows nothing about Gen. Didion's wind deflection theory, yet it demonstrates it routinely. It knows nothing about any type of aerodynamic jump, but it shows them all clearly. It knows nothing about yaw-of-repose or spin-drift, yet it shows them. It knows nothing about Tri-Cyclic Theory, but the computed motions of the spin-axis show it perfectly. In short, the EoM are completely non-analytical in nature, as are their propagations over time. The EoM implemented in PRODAS work as well for air-gun pellets, arrows, handgun bullets, and rifle bullets as they do for the artillery projectiles, rockets, and ICBM's for which it was developed.

I rely upon PRODAS reports to show detailed rifle bullet trajectory data which I then analyze to discover useful relationships. When I discover a useful relationship which predicts PRODAS data results to three or more significant figures, I publish it as an extension of analytical aeroballistic theory. For example, my discovery that horizontal spin-drift is an invariant fraction of the bullet's drop from the projected axis of the bore is accurate to five significant figures to maximum supersonic range for any rifle bullet in the PRODAS data runs which I have on hand. I am working only on flat-firing rifle bullets in the supersonic airspeed regime. Any extension to high-angle firing or transonic or subsonic speed regimes must come later.

Jim Boatright

 

[Deleted member 113831]

For example, my discovery that horizontal spin-drift is an invariant fraction of the bullet's drop from the projected axis of the bore is accurate to five significant figures to maximum supersonic range for any rifle bullet in the PRODAS data runs which I have on hand. I am working only on flat-firing rifle bullets in the supersonic airspeed regime. Any extension to high-angle firing or transonic or subsonic speed regimes must come later.

Jim Boatright

If that means what I think it does, then that is the money shot right there.

 

[Jim Boatright]

I little historical perspective on ELR rifle shooting.

I recall reading somewhere in my bookcase of Civil War military history of an unusual event which occurred late in the war in north Georgia. A Confederate sniper returned to camp one early evening with his trusty English-made 451-caliber Whitworth rifle after a long day of keeping Union artillerymen pinned down. As was his practice, he fired his rifle in the general direction of the enemy so that he could clean it and reload it fresh for the next day's activities. The following day his unit captured a group of Union soldiers who mentioned that one of their own had been struck dead just after sundown by a rifle shot which nobody had heard fired. The Confederate unit knew what had happened. The officers carefully scaled off the map distance to the location of the Union camp as right at five miles, or 8800 yards.

How far would your modern ELR rifle even be able to shoot? That 500-grain swaged lead 451-caliber Whitworth bullet was an excellent subsonic projectile. In early work at Aberdeen Proving Grounds in 1883, the US Army re-invented that bullet for their 45-70 "Trap Door" Springfield rifles. The recruits hated the recoil of that bullet, so they provided 400-grain bullets instead. They rarely hit anything beyond 400 yards anyway. The Buffington rear sights on the M1884 Springfields have a noticeable slant to the left as they are elevated for longer range shots--they had spin-drift and Coriolis effect even back then. My M1884 Springfield was made in 1887 and saw service in the Spanish-American War with Co. K of the 1st US Volunteer Infantry.

 

[christopher.dow]

SD goes beyond the rifle twist rate,


View attachment 6884151
View attachment 6884152

Damn, Frank. That’s quite the heirloom you have there.

 

[TripleBull]

8800 yard kill, lol. I pre-clean launch in your general direction... (Monty Python reference)

Great stuff, Jim.

 

[damoncali]

Damn, Frank. That’s quite the heirloom you have there.

You can get a copy for under a hundred bucks. Amazon is rife with scammers using it to legitimize stolen credit cards, people who would rather put a massive price on an item rather than show it out of stock, and probably more than a few algorithmic pricing programs that just don't work very well.

 

[Lowlight]

Saying the rifles with canted sights accounting for SD seems odd to me when rifles of that era in other disciplines were twisted to the left too See, Lee Enfield.

Right-handed shooters pull shots to the right, it's beyond SD and CE, it's a recoil thing.

Harry Pope made Left Hand Gain Twist barrels for a lot of these rifles and they can found in the NRA Museum, look for any Pope variant and it's all barrel.

This idea that in the 1800s they were figuring SD and CE seems misplaced, I would say it's more a real-world observation and I would bet a lot of it comes from the shooters. How did they measure it beyond shooting it and seeing drift which could easily be shooter drift? Sure a person could say it turned right so it drifted right but all that was a guess.

Launching subsonic bullets back then was more a case of "Hold my beer and Watch this " vs measured accuracy. I would hesitate to call it the birth of ELR

 

[TripleBull]

You can get a copy for under a hundred bucks. Amazon is rife with scammers using it to legitimize stolen credit cards, people who would rather put a massive price on an item rather than show it out of stock, and probably more than a few algorithmic pricing programs that just don't work very well.

Search eBay too. I recently got a copy there for $34 USD shipped. (I just looked at eBay and do not see any listed currently)

 

[damoncali]

This idea that in the 1800s they were figuring SD and CE seems misplaced, I would say it's more a real-world observation and I would bet a lot of it comes from the shooters. How did they measure it beyond shooting it and seeing drift which could easily be shooter drift? Sure a person could say it turned right so it drifted right but all that was a guess.
/QUOTE]

I agree. I haven't seen any mention of it that predates the 20th century. It wasn't until WWII-ish that we even had the capability to utilize the math that was being developed concurrently. Is there even any mention of spin drift prior to the 40's? I can't say whether it was observed first or calculated first, but I think it's safe to say it's a relatively modern discovery.

 

[Lowlight]

No mention of it when I was in the USMC, and even into the 2000s they had it removed from software they were using.

No manual from the 60s to the 90s includes it.

I was also in the first unit to get .50s in the USMC, the SASR ,(Daisy Rifle Design, Iver Johnson Build) no mention there either.

I actually tried looking up WWI manuals on the rifles to see if the manuals mentioned it, never found it.

 

[Deleted member 113831]

No mention of it when I was in the USMC, and even into the 2000s they had it removed from software they were using.

No manual from the 60s to the 90s includes it.

I was also in the first unit to get .50s in the USMC, the SASR ,(Daisy Rifle Design, Iver Johnson Build) no mention there either.

I actually tried looking up WWI manuals on the rifles to see if the manuals mentioned it, never found it.

Not spin drift related but great read on WW1 sniping from the British side.

https://www.amazon.com/Sniping-France-H-Hesketh-Prichard/dp/1514868520

 

[TripleBull]

I think it was ~1850 when Magnus studied it for artillery shells. I have not seen old articles about it specifically regarding small arms ballistics.

 

[damoncali]

Every military source I've seen was much more concerned about artillery than rifles when it came to spin drift. It doesn't surprise me it's not mentioned in rifle courses.

 

[Lowlight]

The Brit Rifles were twisted to the Left they would not mention it unless in that context.

Left-hand Twist barrels were considered correct for Right Handed Shooters, that you can find in discussions of Pope.

 

[Jim Boatright]

The Brit Rifles were twisted to the Left they would not mention it unless in that context.

Left-hand Twist barrels were considered correct for Right Handed Shooters, that you can find in discussions of Pope.

"Drift Firings" of rifles were all the rage in Europe in the 1870's and at Aberdeen in the '80's. Bryan Litz is duplicating them in modern times. Simultaneous firing of essentially identical LH and RH twist rifles at long-range targets with half the horizontal difference in the group centers being declared the spin-drift. The original publication by Coriolis was a paper from 1835. The Coriolis Effects were well understood by the 1880's. The Army and USMC probably did not think them worth bringing up in training manuals and trying to explain them.

 

[damoncali]

"Drift Firings" of rifles were all the rage in Europe in the 1870's and at Aberdeen in the '80's. Bryan Litz is duplicating them in modern times. Simultaneous firing of essentially identical LH and RH twist rifles at long-range targets with half the horizontal difference in the group centers being declared the spin-drift.

I've not seen this documented - do you have a source? I'd be interested in reading up on it. (not the Litz part, the old stuff)

 

[Jim Boatright]

I've not seen this documented - do you have a source? I'd be interested in reading up on it. (not the Litz part, the old stuff)

I tried looking for "drift firings" in my standard references without much luck. The effect was first discovered (about 1800) in attempting to aim accurately with early rifled artillery and naval guns. Poisson, Magnus, and other top mathematicians and physicists attempted explanations of spin-drift in the early and mid-1800's. [They were wrong.] The problem is that for years after each country's military tests, the results were closely held as military secrets. What I have seen (but do not recall where exactly), are long after-the-fact mentions of earlier tests in the introductions to modern works. I believe a History of Aberdeen Proving Grounds showed a wood-block cut of two riflemen firing side by side in drift-firing tests from about 1883. Parallel machine rested barrels with opposite twists were also test-fired. I suggest you look up the Buffington rear sight on the M1884 Springfield for verification. I have an M1884 with such a sight in my collection.

 

[Lowlight]

I have left hand twist rifles at least 4 of them and honestly in terms of SD it’s not noticeable at all. You can “feel” it when you shoot pisitional but it does not change the dope or wind call I use the same method and interchange them effortlessly.

Are you sure the wood blocks are not MV ala the pendulum methods as I fail to see how a wood block plays into it ?

 

[Jim Boatright]

No, I was referring to wood-block printing of artist's sketches for use in book illustrations, before photography was common.

 

[Deleted member 113831]

I wonder if the left hand twist of the old british rifles for right handed shooters had anything to do with the torque produced.

If you've ever shot some of the large caliber 416's or 500's, then you know the torque can be severe. In a rifle with a right hand twist, the gun wants to twist out of your grip to the outside, making it hard to control without a death grip. If the rifling were reversed, then the gun would be torquing into your body.

 

[Diver160651]

Or shoot left handed

 

[Jim Boatright]

I wonder if the left hand twist of the old british rifles for right handed shooters had anything to do with the torque produced.

If you've ever shot some of the large caliber 416's or 500's, then you know the torque can be severe. In a rifle with a right hand twist, the gun wants to twist out of your grip to the outside, making it hard to control without a death grip. If the rifling were reversed, then the gun would be torquing into your body.

Actually, the rifle's torque reaction to spinning-up a RH-twist bullet would be leftward, top side into the body of a right-shoulder rifleman and tightening a RH-threaded barrel into its receiver threads.

The Brits never would say why they used LH rifling and LH receiver threads, but the Northern Hemisphere idea makes sense. Perhaps that is why they had so much trouble in South Africa. The Boers had Mausers with RH-twist barrels.

I do understand why Colt SAA revolvers used LH-twist rifling and had the loading port on the right. Samuel Colt was left-handed.

 

[Deleted member 113831]

Actually, the rifle's torque reaction to spinning-up a RH-twist bullet would be leftward, top side into the body of a right-shoulder rifleman and tightening a RH-threaded barrel into its receiver threads.

We are describing the same torque from different perspectives. From the shooters perspective, the whole gun is trying to twist counterclockwise. The toe of the stock wants to twist away from the body.

 

[TiroFijo]

There is no doubt gyroscopic drift exists, due to yaw of repose. The only doubt is exactly how much (you have to KNOW, not estimate this value at several ranges), and then when is it worth it to account for it.

 

[Deleted member 113831]

There is no doubt gyroscopic drift exists, due to yaw of repose. The only doubt is exactly how much (you have to KNOW, not estimate this value at several ranges), and then when is it worth it to account for it.

For those of us trying to push out to 2000+ yards, the amount of spin drift could potentially equal the width of the 36" target. This is all minutea to most shooters. But if the calculation is half or less as Frank says, then that needs to be discovered and quantified.

Calling wind at these distances and accounting for light and mirage is enough voodoo to deal with. Spin drift, to my thinking should just be a math problem, same as drop. It's just that right now, no one seems to have the definitive answer to that equation.

I'm grateful for Jim's work, maybe he will be the one to bring this answer to us.

 

[damoncali]

It's not a math problem so much as a data problem. Aerodynamic coefficients are simply difficult to nail down with the precision that a lot of ELR shooters want. We know how to calculate drift. Hell - decades ago, they figured out how to calculate the drift when a howitzer projectile is shot 80 degrees into the air, fails to nose over, and falls backwards, reversing the drift on the way down.

It's the uncertainty in that calculation that's being pushed. We can calculate the moments of inertia to near perfection, but the overturning and lift coefficients are still kind of spotty, especially for new ELR bullets. Measuring or calculating those with more certainty is what is needed, not a new way to do the math. The BRL and others figured this out long ago. They just didn't care about this level of detail.