Spin Drift

[Deleted member 113831]

He is not even worth correcting,

Let him think he knows something we don't.

You also seem to trot out the LH twist barrel comment quite often. That only has relevance to the coriolis problem since in the northern hemisphere coriolis is always to the right. It has no relevance in a spin drift discussion because regardless of how spin drift is calculated, it would be identical in either barrel just in opposite directions.

So, if you really do know the difference, I have to wonder why you keep saying these things.

 

[Lowlight]

You also seem to trot out the LH twist barrel comment quite often. That only has relevance to the coriolis problem since in the northern hemisphere coriolis is always to the right. It has no relevance in a spin drift discussion because regardless of how spin drift is calculated, it would be identical in either barrel just in opposite directions.

So, if you really do know the difference, I have to wonder why you keep saying these things.

The point you fool is,

If you spin the bullet to the left, you use the left-hand SD to cancel CE instead of adding to it, 2+2=4 but 2-2=0

Plus if you read up on the turn of the century before they created barreling machines that spun right, they used LH Twist barrels, (see Lee Enfield, not to mention Harry Pope) they considered a LH Twist barrel correct for a Right Handed Shooter

It's not about one or the other, but about both, how you can use them to act together increasing the drift or you can use them to counter each other minimizing it super genius

Try to keep up, I know it is hard,

 

[Lowlight]

PS,

Wonder why MHSA just got a new shipment of LH GAIN TWIST Barrels in, and why I bothered to grab up one to use ... it has nothing to do with nothing.

Mark Chanlin also does LH Twist barrels, the fact Bartlein is producing them in quantity now and people are using them should tell you something.

 

[Deleted member 113831]

PS,

Wonder why MHSA just got a new shipment of LH GAIN TWIST Barrels in, and why I bothered to grab up one to use ... it has nothing to do with nothing.

Mark Chanlin also does LH Twist barrels, the fact Bartlein is producing them in quantity now and people are using them should tell you something.

It tells me that more people are interested in cancelling some spindrift with an offsetting coriolis effect. I don't know how you figure that proves they are equal. In a 308 that would reduce spin drift effect from 0.3 mils to 0.2 mils, a %33 reduction isn't to be sneezed at. With a sleeker bullet it would cancel 0.2 mils to a 0.1mil difference, %50 is even better!....still doesn't prove the effects are equal, just that people will pay to not have to do math.

You do realize that the AB math was verified on a 1000 yard range with live fire right? Instrumentation is set up at intervals along the bullet path to factor out wind speed and direction. In a few cases, identical loads were shot from identical rifles, at the same moment, the only difference being the direction of twist. The distance of the group centers from point of aim was the same in thier respective directions. It wasn't 3 inches.

 

[Lowlight]

I never said they were equal,

Why don't you read the thread and then look at the reference material I provided, clearly you cannot follow along too well.

The fact you can "reduce" these two drifts by working them against each other vs compounding them as we do now, (out of laziness) is clearly my point. The farther you shoot, the more they will offset each other.

Not to mention the other point, these published numbers are incorrect because they use old data and poor scientific methods are also part of the point. There is more that goes into it and the effects are much smaller than advertised.

I never turn on SD, I never turn on CE in any software with the ability and it served me fine for longer than most have been shooting is another clue in all this.

What about the wind, you realize the wind has an effect on the amount of SD depending on the direction, combined with the direction of SD.

You're solver is not calculating shit, it's just giving you a flat rate value intended to be close enough.

All of Pesja's books go into the myth-busting details of this stuff,

 

[Lowlight]

I especially like his mocking tone with guys who invest in spirit levels as he puts it in order to combat cant,

 

[Deleted member 113831]

I never said they were equal,

Why don't you read the thread and then look at the reference material I provided, clearly you cannot follow along too well.

The fact you can "reduce" these two drifts by working them against each other vs compounding them as we do now, (out of laziness) is clearly my point. The farther you shoot, the more they will offset each other.

Not to mention the other point, these published numbers are incorrect because they use old data and poor scientific methods are also part of the point. There is more that goes into it and the effects are much smaller than advertised.

I never turn on SD, I never turn on CE in any software with the ability and it served me fine for longer than most have been shooting is another clue in all this.

What about the wind, you realize the wind has an effect on the amount of SD depending on the direction, combined with the direction of SD.

You're solver is not calculating shit, it's just giving you a flat rate value intended to be close enough.

All of Pesja's books go into the myth-busting details of this stuff,

When you said 2+2=4, and 2-2=0, I guess I wrongly assumed 2=2 (meaning SD was equal to CE in case you are having trouble following along). So maybe the math IS your problem.

This "old" data you keep referring to...you mean like the handful of years since Strelok and AB came out? 'Cause like I said,( in case you aren't following along) all this math has been revisited, revised and verified. There are thousands of people running AB and Strelok out to ridiculous distances and finding it to be spot on. It seems highly unlikely they all could be suffering from the same delusion.

You keep saying that you don't use it and get good hits...that doesn't surprise me at all. If you've never used it, then what you've done is calibrate your brain to include it into your wind solution. You are accounting for it, you just don't realize it. At 1000 yds with a 6.5 creedmoor, 1mph wind is a difference of 0.2 mils. So if I dial spindrfit and call it a 5 mph wind and you don't dial it but call it a 6 mph wind, then we will pretty much hit in the same place. But that still doesn't change the fact that it is actually a 5 mph.

It also seems that with the rise of ELR, (and now UR "unlimited range" 2000+ yds) any bullshit that has passed as a myth concerning any of these effects is quickly being burned away. First round hits at 1500+ yards are reality, it is happening right now. You don't get there by miscalculating anything. There are still offsetting factors but they don't completely cancel out. Inside 1K yards, you know you can get away with doing some stupid shit and still get hits. Step out to 1500+ and you better know what is what.

The bit in the book about the "myth" of close wind being more important than far wind, that depends on how you are doing the calculation. If you are talking about linear distance, then yeah far wind moves the bullet further because it has more time to act on it (the bullet is slowing down). But if you look at it as an angular distance, the way we determine distance through the scope, it does not. The shortened amount of time left to the target will not amount to as much angular distance on the far end.

That bit in the book about canting....I get that he was criticizing those who are overly worried about it, but that sounded retarded. He sounds like the Alex Jones of ballistics.

 

[djarecke]

When you said 2+2=4, and 2-2=0, I guess I wrongly assumed 2=2 (meaning SD was equal to CE in case you are having trouble following along). So maybe the math IS your problem.

That bit in the book about canting....I get that he was criticizing those who are overly worried about it, but that sounded retarded. He sounds like the Alex Jones of ballistics.

Now that's some funny stuff right there.

But let me summarize what you need to know about spin drift: Lowlight said don't worry about it. Therefore, we don't need to worry about it. To solidify this position, even some book said so!

All done. Spin drift is to be mocked, discounted, and had a carbonated drink named after it. And if you choose to add a click or two at 1000 for it, you're an ass clown.

Next topic...

 

[Lowlight]

My private range has targets every 100 yards to 1 mile from the firing line, and it goes back even farther.

In November I shot to 4000 yards, 3250, 2600, etc, the AB Solution at 3250 called for 5 mils of correction with SD and CE, we were using 1.5 to hit the target, go figure. I must have calculated that in to hit shit vs missing.

I graduated sniper school without it too, wonder why no USMC manuals include it, hmmm, interesting. They even asked it to be removed from some of their software.

I think I know what I am doing at distance, you keep on just repeating the same old stuff over and over, it makes you sound smart. Your 3DOF calculator is really knocking it out of the park, so keep swinging Petey

 

[Lowlight]

PS, the Author of the Book, dead now, but was doing this a long, long time,

In fact, his formulas and methods are what power Field Firing Solutions and CoidBore both of which pre-date every App out there including your favorites. They are generally considered much better at providing solutions vs the competition and don't require the same level of Truing, or at least you don't do it in the same, poor fashion.

The math, by the way, was to make it easy for you, I was not sure you could understand adding and subtracting so I figured with 2 + 2 you can solve 4 and with 2 - 2 you might be able to count on one hand to get 0.

 

[Deleted member 113831]

My private range has targets every 100 yards to 1 mile from the firing line, and it goes back even farther.

In November I shot to 4000 yards, 3250, 2600, etc, the AB Solution at 3250 called for 5 mils of correction with SD and CE, we were using 1.5 to hit the target, go figure. I must have calculated that in to hit shit vs missing.

I graduated sniper school without it too, wonder why no USMC manuals include it, hmmm, interesting. They even asked it to be removed from some of their software.

I think I know what I am doing at distance, you keep on just repeating the same old stuff over and over, it makes you sound smart. Your 3DOF calculator is really knocking it out of the park, so keep swinging Petey

Without seeing the inputs and conditions it is impossible to know where you went wrong at 3250.

You keep bringing up the sniper school thing too. In sniper school the vast majority of shooting is done under 800 yards and E type silhouettes are 20" wide and 40" tall. The ballistics portion of sniper school is basic in the extreme. After all, they have to teach it to marines. Saying you know about ballistics because of sniper school is like saying you know martial arts because you got your orange belt in Taekwondo.

Latest word I heard on spin drift in the schools is that it is being taught again.

 

[Diver160651]

[QUOTE="Skookum, post: 6962717, member: 113831">>There are thousands of people running AB and Strelok out to ridiculous distances and finding it to be spot on. It seems highly unlikely they all could be suffering from the same delusion.

>>SNIP<<
It also seems that with the rise of ELR, (and now UR "unlimited range" 2000+ yds) any bullshit that has passed as a myth concerning any of these effects is quickly being burned away. First round hits at 1500+ yards are reality, it is happening right now. You don't get there by miscalculating anything. There are still offsetting factors but they don't completely cancel out. Inside 1K yards, you know you can get away with doing some stupid shit and still get hits. Step out to 1500+ and you better know what is what.
[/QUOTE]

Very, Very few people have taken the time to vet the calculators from zero out past 2k at the important parts along the way.. Some of the new UR guys don't even have a clue what there gun does as 300 600 etc. It has become very much an F-class event.

The very fact that someone uses a segment of a AB curve that has been tuned to real drop in a limited area does NOT mean the calculator worked click accurate.

It is frustrating that this flipping myth keeps getting put out there... now back to drinking my over priced SD soda

 

[sobrbiker883]

Until I can see someone repeatedly shoot the difference under field conditions at distance I will continue to not worry about it.
It’s one of the many chunks of minutiae that get lost in the noise of reality that too many spend too much time trying to figure out in the webworld, instead of relying on what their rifle tells them...

 

[Deleted member 113831]

[/QUOTE]Very, Very few people have taken the time to vet the calculators from zero out past 2k at the important parts along the way.. Some of the new UR guys don't even have a clue what there gun does as 300 600 etc. It has become very much an F-class event.

True, but I never said it was the same people doing it all. The longrange hunters are carrying the ball to a mile.

The very fact that someone uses a segment of a AB curve that has been tuned to real drop in a limited area does NOT mean the calculator worked click accurate.

Also true, AB has some work to do in the subsonic range, but with the ELR cartridges in current use, that range starts past 2000 yards. I'm not a Bryan Litz fanboy, but if something is working I'll use it.

 

[Diver160651]

I’m sorry, but your response shows you do not know what I am talking about.

If you routinely shot out in the 25 mill range you would know what I’m talking about.

 

[morganlamprecht]

Very, Very few people have taken the time to vet the calculators from zero out past 2k at the important parts along the way.. Some of the new UR guys don't even have a clue what there gun does as 300 600 etc. It has become very much an F-class event.

The very fact that someone uses a segment of a AB curve that has been tuned to real drop in a limited area does NOT mean the calculator worked click accurate.

It is frustrating that this flipping myth keeps getting put out there... now back to drinking my over priced SD soda

ive seen a few examples of this

 

[damoncali]

The Spin Drift Argument, Simplified Edition:

Q: Is it real?
A: Yes.

Q: Does it matter?
A: Define "matter".

Q: How do you calculate it?
A: It's complicated.

Q: Did you know there is actually a thing called spindrift soda?
A: Yes, and that's hilarious.

 

[Diver160651]

I bet Gustave “C” would have loved a trendy soda named after him..

 

[Lowlight]

he is a troll and regurgitator chasing me around again, eventually, he won't be able to stop himself and just get banned again.

He is working on his next ban I am sure, I love how all of the sudden Military Service doesn't count, I am sure the training years at Rifles Only don't count either for him, nor the insight I get like when Hornady invited to shoot the 4DOF and Doppler. That ballistic class by Dave Emry is lame compared to what is in Strelok.


I want to see the data used to calculate the SD in his chosen solver, I want to see where they measured and used the different bullets to "calculate" his answer. Show me where you input your bullet's data, and by that, I mean everything beyond Bullet Length

I have to hit the VA, when I get back I will make one post and stop the nonsense in the meantime here, try not to cum in your pants

 

[CrazyHorse_mk14]

I drank too much SD one time and ended up with a STD.

 

[CrazyHorse_mk14]

I aimed at the good looking chick but forgot which way the earth rotates, hit the fat ugly one instead ..it was just a few clicks off

 

[Diver160651]

I aimed at the good looking chick but forgot which way the earth rotates, hit the fat ugly one instead ..it was just a few clicks off

Dammit Jim, Spock here, don’t you know that’s not SD? LoL

 

[damoncali]

I heard if you put one foot on the ground, spin drift drops in half. But yeah, that's mostly Coriolis.

 

[CrazyHorse_mk14]

Dammit Jim, Spock here, don’t you know that’s not SD? LoL

Don’t blame me for not knowing ! The stupid military didn’t put it in the manuals!

 

[Long Range 338]

Without seeing the inputs and conditions it is impossible to know where you went wrong at 3250.

You keep bringing up the sniper school thing too. In sniper school the vast majority of shooting is done under 800 yards and E type silhouettes are 20" wide and 40" tall. The ballistics portion of sniper school is basic in the extreme. After all, they have to teach it to marines. Saying you know about ballistics because of sniper school is like saying you know martial arts because you got your orange belt in Taekwondo.

Latest word I heard on spin drift in the schools is that it is being taught again.

Ok so you've been berating Lowlight, disregarding out of hand his experience and education, and telling him how wrong he is so that you can garner some attention. Now please bless us with your incredible credentials and experience so that we may learn from you.........

 

[_Windrider_]

Ok so you've been berating Lowlight, disregarding out of hand his experience and education, and telling him how wrong he is so that you can garner some attention. Now please bless us with your incredible credentials and experience so that we may learn from you.........

call of duty and Tom Clancy ghost recon. Shit is as real as it gets

 

[Lowlight]

The numbers in the Jim Boatright are probably the best starting point and even those fluctuate all over the map.

if you decipher the data a bit, you can see where combined with a number of .30 Cal bullets most are around 9" of SD based on a variety of methods, the key to this is looking at the data used to calculate and realize you are not calculating anything at all because we fail to input this much data. All the variations over emphasis SD, that point is clear.

The one glaring variation is the 173gr 30 cal, and why is it SO DIFFERENT .... easy Muzzle velocity.

Look at the speed variations

At 1000 yards the 173gr bullet is still 1800fps vs the other 30 Cals that are closer to 1200fps, everything close to 1200fps is close to 9" of predicted, yet the one that 1800fps is 3" of SD

Huge variation and a huge amount of data necessary to come anywhere close to calculating this.

Nowhere are you are entering this much bullet data, you get one input, bullet length, that is it.

Speed is proving to be more and more a factor when you look at the numbers, and you can, in fact, go lighter to increase the speed and reduce a measurable amount of error or in this case drift

Even with Aero Jump, look at how ColdBore handles the inputs

So the Alex Jones of Ballisticians, who Gus Ruiz uses a baseline, Pesja is in ColdBore's DNA, it has you actually calculating things none of this other software does. It needs more data, hence better results.

Clearly, it matters, when you look at the papers on the subject. The error in SD using multiple methods can be as much as 3" of error between them.

I still think they are overdoing it to a certain extent because of the speed issue, we are running faster than before. The formulas were modeled first with artillery and next with slow moving 30 cals that were under 2600fps, actually, a 168 going 2550-fps, bad bullet with slow MV.

This is why the USMC ignored it because they said clearly it only mattered after Transonic and for that you have a radio.

I don't know how they figured the actual, I don't believe it describes the firing method to obtain a number, but we have numbers that don't jive to any predictions and all those are more than actual.

This is not settled science and not everyone agrees on the method or the real world value, if your speed is anywhere near that of the 173gr example we fall right into that 3" mark even though the software will tell you 9" to 12" at 1000 yards. Everyone who wastes their time with it wants to add in .2 to .3 Mils of drift.

if the new methods and models here calculates 7" and you say 10" and the book with 1950s data says 9", what is the percentage of error if they are 2"- 3" off the mark? That is the reality of it, you ain't figuring shit, they are giving you a number they hope won't hurt and with the majority of right-handed shooters making right-handed shooter errors to the right, this is why you believe it works. That extra 3" of drift on average is from you being a poor marksman.

It's 3" of SD and 6" of Shooter Drift or trigger control error reduction.

 

[LastShot300]

Great post, black on white. One of those posts that need to be in the library for future reference. And the paper by Boatright and Ruiz puts all the truth over the table and destroys the usual flat rate, AB and others made us to believe in first place.

 

[Jim Boatright]

I had not found this thread earlier, or would have commented sooner. What fun. I am revising that Spin-Drift paper along with Gustavo to incorporate a much better estimator of the bullet's second moment of inertia ratio, Iy/Ix. This value runs about 6 to 12 for jacketed rifle bullets and about 12 to 14 for monolithic copper-alloy bullets up to 5.6 calibers in length. The new estimator comes from the cone-on-cylinder bullet model used by Dr. Kneubuehl of Switzerland [See Resources Section.] It is better than my "slender rod" approach developed for this Spin-Drift paper. I wish I had thought of it myself. We will post it here when it is ready and cross-checked as best we can. With the much improved Iy/Ix calculations, our SD calculations run about 2(+) inches less than Bryan's at 1000 yards for most bullets and firing conditions. This improvement will also be incorporated into the much more significant CWAJ calculations for use in the field.

Jim Boatright

 

[Deleted member 113831]

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"

 

[TripleBull]

I didn't need to know that you were also obsessed with fairies.

 

[lte82]

I had not found this thread earlier, or would have commented sooner. What fun. I am revising that Spin-Drift paper along with Gustavo to incorporate a much better estimator of the bullet's second moment of inertia ratio, Iy/Ix. This value runs about 6 to 12 for jacketed rifle bullets and about 12 to 14 for monolithic copper-alloy bullets up to 5.6 calibers in length. The new estimator comes from the cone-on-cylinder bullet model used by Dr. Kneubuehl of Switzerland [See Resources Section.] It is better than my "slender rod" approach developed for this Spin-Drift paper. I wish I had thought of it myself. We will post it here when it is ready and cross-checked as best we can. With the much improved Iy/Ix calculations, our SD calculations run about 2(+) inches less than Bryan's at 1000 yards for most bullets and firing conditions. This improvement will also be incorporated into the much more significant CWAJ calculations for use in the field.

Jim Boatright

While I'm not sure I can call wind or hold inside 2" at 1000 yards, the take away for me is that you are saying is that SD is relevant, despite being slightly less than what AB might calculate.

I've also read your paper on CWAJ, and my takeaway from it was that AJ should only be factored based on the wind within the first 10 yards, and that for the bullets I typically shoot (SG of 1.7 ish) litz approximation is close enough. So if I'm shooting from a sheltered position, it's not a big factor, but if I'm in an open field, it *is* a factor. I also find it interesting though that with SG's around the 1.5-1.6 range, which *can* happen where I shoot in cold weather / high pressure, you are calculating *more* AJ than Litz. In other words, it sounds like you would *not* agree that you can simply ignore any AJ elevation effects due to crosswinds, but you need to check your individual situation.

The question though is how is your new Iy/Ix going to affect AJ calculations? Will it estimate less? Maybe make it match up a little more to AB's projections? Also, what are your thoughts on Coriolis effect? Is it worthwhile to keep that in your solution? Sorry for so many questions, it's not every day I get to ask the guy that literally is writing the book on it...

 

[damoncali]

I had not found this thread earlier, or would have commented sooner. What fun. I am revising that Spin-Drift paper along with Gustavo to incorporate a much better estimator of the bullet's second moment of inertia ratio, Iy/Ix. This value runs about 6 to 12 for jacketed rifle bullets and about 12 to 14 for monolithic copper-alloy bullets up to 5.6 calibers in length. The new estimator comes from the cone-on-cylinder bullet model used by Dr. Kneubuehl of Switzerland [See Resources Section.] It is better than my "slender rod" approach developed for this Spin-Drift paper. I wish I had thought of it myself. We will post it here when it is ready and cross-checked as best we can. With the much improved Iy/Ix calculations, our SD calculations run about 2(+) inches less than Bryan's at 1000 yards for most bullets and firing conditions. This improvement will also be incorporated into the much more significant CWAJ calculations for use in the field.

Jim Boatright

Why not just calculate the moments of inertia in a more detailed way (truncated cone for boattail, cylinder for bearing surface, ogival solid for nose.)? You only need a few bullet dimensions to do it. I think the folks that care enough about this level of precision wouldn’t mind inputting a few more bullet details. The math and geometry are a pain in the rear (I’ve done it), but once it’s done, it’s done. Between that and intlift, I’d think you could get a pretty accurate number for any sane bullet configuration.

 

[TiroFijo]

My take is that serious, extensive, in depth (OK, expensive) studies with doppler radar and ranges with advanced wind measured downrange (or advanced wind barriers) are needed with the new modern bullets that are being used/proposed for ELR.
These tests and studies should ideally be carried out by an independant entity that does is not one of the bullet/ammo makers, like the US Army in the Aberdeen or Yuma PGs...

 

[Lowlight]

they have to be shot from a fixture too, because there is too much shooter in all this

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

 

[Jim Boatright]

While I'm not sure I can call wind or hold inside 2" at 1000 yards, the take away for me is that you are saying is that SD is relevant, despite being slightly less than what AB might calculate.

I've also read your paper on CWAJ, and my takeaway from it was that AJ should only be factored based on the wind within the first 10 yards, and that for the bullets I typically shoot (SG of 1.7 ish) litz approximation is close enough. So if I'm shooting from a sheltered position, it's not a big factor, but if I'm in an open field, it *is* a factor. I also find it interesting though that with SG's around the 1.5-1.6 range, which *can* happen where I shoot in cold weather / high pressure, you are calculating *more* AJ than Litz. In other words, it sounds like you would *not* agree that you can simply ignore any AJ elevation effects due to crosswinds, but you need to check your individual situation.

The question though is how is your new Iy/Ix going to affect AJ calculations? Will it estimate less? Maybe make it match up a little more to AB's projections? Also, what are your thoughts on Coriolis effect? Is it worthwhile to keep that in your solution? Sorry for so many questions, it's not every day I get to ask the guy that literally is writing the book on it...

I need to amend your takeaway about CWAJ somewhat. CWAJ is a one-time transient effect which occurs when the rifle bullet first encounters a typically horizontal (laminar wind flow) crosswind. If you are shooting from inside a building through an open window, it is the wind outside the window that the bullet first encounters. Gustavo and I wrote the paper assuming field shooting from a supported outdoor position usually near the ground. I must emphasize again that CWAJ really has nothing to do with the overall wind calling problem, even if you are willing to assume the wind at your firing point holds all the way to your target. We have not yet run the numbers for CWAJ situations with the improved Iy/Ix ratio estimator.

I have seriously looked into simplifying the Coriolis Effect for riflemen several years ago. I concluded that Bryan's approach is suitable. Don't forget the separately estimated vertical effect also. I recommend entering your latitude and firing azimuth and letting your firing solution computer calculate those aiming corrections for long shots. Otherwise, one should rely upon the law of conservation of angular momentum to get the significant Coriolis effect directions correct. If you are in the Northern Hemisphere, a shot northward is "downhill" toward the North Pole [The bullet is getting nearer the earth's axis.], and conservation of momentum says the free flight (orbit) of the bullet must rotate eastward faster that it was at launch for rightward deflection. Reverse for shooting southward, and your westward deflection is still rightward. If you are shooting eastward from any location away from the poles, your launch velocity adds to the eastward velocity of your firing point on the rotating earth, and your shot will go high due to its increased orbital speed, so hold lower. Reverse for shooting westward, and hold higher.

I should have mentioned in my comments about spin-drift that the horizontal spin-drift trajectory is some constant fraction (between 1 percent and 2.4 percent) of the bullets "drop from the bore axis" at any long range. In other words, the wind-free, Coriolis-free, horizontal trajectory looks just like a small fraction of the vertical trajectory, but rotated 90 degrees about the projected bore axis. Both curvatures are ultimately caused by firing through the same gravitational field. The faction is about 1 to 1.2 percent for modern monolithic ELR bullets, and 2 to 2.4 percent for shorter, fatter jacketed, lead-core bullets. The ratio of drift to drop rapidly approaches this particular fraction as a limit beyond about 150 yards range. The trick is then to calculate the fraction accurately for any given rifle bullet and firing conditions. This observation explains the fact that higher velocity bullets have less spin-drift at long ranges--they have less drop.

Jim Boatright

 

[Jim Boatright]

My take is that serious, extensive, in depth (OK, expensive) studies with doppler radar and ranges with advanced wind measured downrange (or advanced wind barriers) are needed with the new modern bullets that are being used/proposed for ELR.
These tests and studies should ideally be carried out by an independant entity that does is not one of the bullet/ammo makers, like the US Army in the Aberdeen or Yuma PGs...

The Army is awaiting you ELR guys demonstrating what works before they bother with their own testing. I offered them my bullet patent, but they did not even reply.

Jim Boatright

 

[Jim Boatright]

Why not just calculate the moments of inertia in a more detailed way (truncated cone for boattail, cylinder for bearing surface, ogival solid for nose.)? You only need a few bullet dimensions to do it. I think the folks that care enough about this level of precision wouldn’t mind inputting a few more bullet details. The math and geometry are a pain in the rear (I’ve done it), but once it’s done, it’s done. Between that and intlift, I’d think you could get a pretty accurate number for any sane bullet configuration.

The cone-on-cylinder model shows promise of yielding Iy/Ix value within 0.5 percent of the numerically integrated values for modern solid monolithic ELR bullets, using the bullet descriptors already being input by the user. That is exceptionally good performance for aeroballistics work. The main difficulty in calculating these secondary effects (CWAJ and spin-drift) is requiring the user to specify the bullet mass properties accurately enough, particularly for rifle bullets made of non-homogeneous materials and having significant hollow cavities within. If we had those mass properties, we could just run a field version of PRODAS and use the full 6-DoF firing solution. Someday, I hope that bullet manufacturers will upload those aeroballistic parameters for each new bullet into a shared database which will then be available in everyone's field computers. We already have suitably powerful portable computers to run 6-DoF solutions for each long-range shot. Until then, we struggle along making increasingly accurate approximations and requiring ever more data inputs.

Jim Boatright

 

[LastShot300]

I need to amend your takeaway about CWAJ somewhat. CWAJ is a one-time transient effect which occurs when the rifle bullet first encounters a typically horizontal (laminar wind flow) crosswind. If you are shooting from inside a building through an open window, it is the wind outside the window that the bullet first encounters. Gustavo and I wrote the paper assuming field shooting from a supported outdoor position usually near the ground. I must emphasize again that CWAJ really has nothing to do with the overall wind calling problem, even if you are willing to assume the wind at your firing point holds all the way to your target. We have not yet run the numbers for CWAJ situations with the improved Iy/Ix ratio estimator.

I have seriously looked into simplifying the Coriolis Effect for riflemen several years ago. I concluded that Bryan's approach is suitable. Don't forget the separately estimated vertical effect also. I recommend entering your latitude and firing azimuth and letting you firing solution calculate those aiming corrections for long shots. Otherwise, one should rely upon the law of conservation of angular momentum to get the significant Coriolis effect directions correct. If you are in the Northern Hemisphere, a shot northward is "downhill" toward the North Pole, and the free flight (orbit) of the bullet must rotate eastward faster that it was at launch for rightward deflection. Reverse for shooting southward, and your eastward deflection is now leftward. f you are shooting eastward from any location away from the poles, your launch velocity adds to the eastward velocity of your firing point on the rotating earth, and your shot will go high due to its increased orbital speed, so hold lower. Reverse for shooting westward, and hold higher.

I should have mentioned in my comments about spin-drift that the horizontal spin-drift trajectory is some constant fraction (between 1 percent and 2.4 percent) of the bullets "drop from the bore axis" at any long range. In other words, the wind-free, Coriolis-free, horizontal trajectory looks just like a small fraction of the vertical trajectory, but rotated 90 degrees about the projected bore axis. Both curvatures are ultimately caused by firing through the same gravitational field. The faction is about 1 to 1.2 percent for modern monolithic ELR bullets, and 2 to 2.4 percent for shorter, fatter jacketed, lead-core bullets. The ratio of drift to drop rapidly approaches this particular fraction as a limit beyond about 150 yards range. The trick is then to calculate the fraction accurately for any given rifle bullet and firing conditions. This observation explains the fact that higher velocity bullets have less spin-drift at long ranges--they have less drop.

Jim Boatright

Thanks Jim and Gus for keeping this work updated, this is serious stuff not the usual utterly simplifications we are used to.

 

[lte82]

Jim, thanks for your reply. So if the bullet has a transient shift in the first 10 yards of encountering crosswind, and the shift has an absolute value, the further that shift occurs away from the shooter the less effect it has down range. IE, if the crosswind is effective at the shooter, say you have a .3 moa shift by yard 10, the aerodynamic jump was .03". So if the bullet doesn't encounter crosswind until 100 yards away, the .03" shift only affects the bullet .03 moa. So basically the more shelter you have the less effect cwaj has on the solution. I'm just theorizing that's why some guys see the shift and others don't.

Interesting enough, I shot next to the former Marine high power coach last year, and they actually had a rule of thumb for elevation shift due to CWAJ. 1/4 moa per 10 mph. That correlates pretty dang close to your math...

 

[sandwarrior]

The Army is awaiting you ELR guys demonstrating what works before they bother with their own testing. I offered them my bullet patent, but they did not even reply.

Jim Boatright

ha ha, yeah their opinion is Why change? by the time they change lazers will be in vogue. 7.62 for long range and 5.56 for all the rest. Nothing else needed... ...

 

[TiroFijo]

Bryan Litz has been awarded a .mil contract "to advance the state of the art in long range rifle shooting"

https://www.ammoland.com/2018/03/applied-ballistics-wins-military-rd-contract/#axzz5DtmJ5ldS

This of course includes doppler radar testing, yadda, yadda... (I think all current US sniper rounds have fairly extensive LR testing, including doppler radar testing to determine secundary ballistic effects, etc.).

But I wonder what calibers and bullets are going to be tested. The current .mil LR sniper rounds are not state of the art by any means.

 

[Lowlight]

Others are using doppler, some longer than others,

Look at the images and ranges, when I shot over the Hornady Doppler we tracked my rounds to 2000 yards, and determined our data off that

The Doppler stuff ( and both Hornady and AB have the same unit) does not show SD, they used Spark Range Data for that as there is a difference

 

[Deleted member 113831]

I need to amend your takeaway about CWAJ somewhat. CWAJ is a one-time transient effect which occurs when the rifle bullet first encounters a typically horizontal (laminar wind flow) crosswind. If you are shooting from inside a building through an open window, it is the wind outside the window that the bullet first encounters. Gustavo and I wrote the paper assuming field shooting from a supported outdoor position usually near the ground. I must emphasize again that CWAJ really has nothing to do with the overall wind calling problem, even if you are willing to assume the wind at your firing point holds all the way to your target. We have not yet run the numbers for CWAJ situations with the improved Iy/Ix ratio estimator.

I have seriously looked into simplifying the Coriolis Effect for riflemen several years ago. I concluded that Bryan's approach is suitable. Don't forget the separately estimated vertical effect also. I recommend entering your latitude and firing azimuth and letting your firing solution computer calculate those aiming corrections for long shots. Otherwise, one should rely upon the law of conservation of angular momentum to get the significant Coriolis effect directions correct. If you are in the Northern Hemisphere, a shot northward is "downhill" toward the North Pole [The bullet is getting nearer the earth's axis.], and conservation of momentum says the free flight (orbit) of the bullet must rotate eastward faster that it was at launch for rightward deflection. Reverse for shooting southward, and your westward deflection is still rightward. If you are shooting eastward from any location away from the poles, your launch velocity adds to the eastward velocity of your firing point on the rotating earth, and your shot will go high due to its increased orbital speed, so hold lower. Reverse for shooting westward, and hold higher.

The faction is about 1 to 1.2 percent for modern monolithic ELR bullets, and 2 to 2.4 percent for shorter, fatter jacketed, lead-core bullets. The ratio of drift to drop rapidly approaches this particular fraction as a limit beyond about 150 yards range. The trick is then to calculate the fraction accurately for any given rifle bullet and firing conditions. This observation explains the fact that higher velocity bullets have less spin-drift at long ranges--they have less drop.

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%

 

[Deleted member 10043]

Are we in the Northern Hemisphere?

 

[Deleted member 113831]

Are we in the Northern Hemisphere?

If you are asking me, I'm in WA state.

 

[Lowlight]

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,

They have a lead replacement designed just for this,

Why Use Technon® in Lead Replacement Compounds?

Technon® offers many advantages to compounders:

Technon® has a spheroidal grain structure. This makes for a faster and better mix
Technon® can save energy during the mixing process
Technon® has a Tap-density of 11.75 g/cc, which is higher than any density filler material currently available
Compounds containing Technon® are easier to inject, and better protect the injection machinery
Technon® has a large particle size, opening the door to many new applications, uses, and formulations, which are otherwise protected by patents.

What Are Some Lead Replacement Applications of These New Materials?

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.

 

[Deleted member 113831]

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 2.1 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,

Why Use Technon® in Lead Replacement Compounds?

Technon® offers many advantages to compounders:

Technon® has a spheroidal grain structure. This makes for a faster and better mix
Technon® can save energy during the mixing process
Technon® has a Tap-density of 11.75 g/cc, which is higher than any density filler material currently available
Compounds containing Technon® are easier to inject, and better protect the injection machinery
Technon® has a large particle size, opening the door to many new applications, uses, and formulations, which are otherwise protected by patents.

What Are Some Lead Replacement Applications of These New Materials?

Ammunition: Projectiles and shots,

I am willing to be 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.

You raise an interesting point about the core material being the issue. If the bullet changes shape after leaving the barrel, and does so unpredictably from rifle to rifle, then it would be impossible to calculate accurately.

Jim's post opened my eyes to SD being at least in part, connected to drop. Less drop means less lag time, less lag time means less time to drift.

But I always figured that another determining factor was the location of the center of pressure on the ogive. As the ogive gets sleeker, the center of pressure moves further toward the tip creating a longer overturning moment arm. This is of course why we have to spin them faster to increase axial rigidity. But directly opposite the center of pressure is a low pressure area creating drag. I think of it as a bubble that the bullet nose is constantly trying to roll to the right of ( right hand twist ).

So the pointier bullets are not only decreasing the amount of time they are rolling for a given distance, they are rolling to the right of a considerably smaller bubble.

All that aside, If I can predict my bullet SD from my particular rifle to within .1 moa as in the case you cited above. I will be happy. I don't care where the info comes from. In fact, if I can figure it as a percentage of drop and determine what my real world percentage actually is, then I don't need or want the ballistic calculator to do that. I will figure that into my firing solution myself. All I really want from a ballistic calculator is an accurate drop. If I can get that, the rest is on me.

 

[Greg Langelius *]

I also just ordered it, and I had to hurry, 'cause it said there was only one copy left...

No poo...! Arriving Wednesday, on Prime.

Greg

 

[Greg Langelius *]

Reading the pictured text about near/far crosswinds was especially interesting.

As I understand it, winds at any distance cause the same degree of deflection, but those occurring sooner cause the departure on a new baseline direction to act over a larger portion of the trajectory, and also compound the effects of subsequent deflections.

Not the same as nearer, more effect, and farther, less effect; but maybe essentially resulting in a very similar outcome.

Greg