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Range Report Spindrift Calculation??
- Thread starter ChadTRG42
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- calculation spindrift
Re: Spindrift Calculation??
Lowlight,
For goodness sake make this go away...use the force Luke, or at least use your delete post option. No if you did that someone else would just start a new post.
Guys I'm out of popcorn and my neck is tired from watching this ping pong ball go back and forth. You’re trying to make a mountain out of a mole hill. Does spin drift exist, Yup! Do black holes exist in the universe, Yup! Neither one is worth this much bantering. The majority of long range shooters who shoot over 1500 yards consciously or subconsciously compensate for spin drift with windage adjustments. Can it be calculated for in theory yes, but there are too many variables in play for truly accurate calculations, variable speed cross winds come to mind.
I’d love to see someone take the ABC ballistic program only (not the entire Doppler Radar set up) to Storm Mountain training center in Elk Garden West VA. Use the program to calculate a first round hit at 2000 yards, don’t forget to factor in spin drift! I’m not sure if Rod’s longest range makes it to 2K but take his furthest shot. There are more cross winds blowing at different speeds and from multiple directions than you can shake a stick at. If you’ve never shot there you just can’t fully understand the environmental conditions that come into play. Once you see all these cross winds, spin drift or thought of spin drift wouldn’t even enter your mind.
Now everyone shake hands and agree to disagree and can we please move on?
Lowlight,
For goodness sake make this go away...use the force Luke, or at least use your delete post option. No if you did that someone else would just start a new post.
Guys I'm out of popcorn and my neck is tired from watching this ping pong ball go back and forth. You’re trying to make a mountain out of a mole hill. Does spin drift exist, Yup! Do black holes exist in the universe, Yup! Neither one is worth this much bantering. The majority of long range shooters who shoot over 1500 yards consciously or subconsciously compensate for spin drift with windage adjustments. Can it be calculated for in theory yes, but there are too many variables in play for truly accurate calculations, variable speed cross winds come to mind.
I’d love to see someone take the ABC ballistic program only (not the entire Doppler Radar set up) to Storm Mountain training center in Elk Garden West VA. Use the program to calculate a first round hit at 2000 yards, don’t forget to factor in spin drift! I’m not sure if Rod’s longest range makes it to 2K but take his furthest shot. There are more cross winds blowing at different speeds and from multiple directions than you can shake a stick at. If you’ve never shot there you just can’t fully understand the environmental conditions that come into play. Once you see all these cross winds, spin drift or thought of spin drift wouldn’t even enter your mind.
Now everyone shake hands and agree to disagree and can we please move on?
Re: Spindrift Calculation??
Brown Dog: I thiink we are in very good agreement--perhaps violently so.....
The difference, here, is the same as the difference between "trying to figure out what the physics is", and then "using that physics to solve a dataset".
In order to develop a full ballistics model, you must be able to do a 6-DOF calculation and fit many data points perhaps several different kinds of projectiles and distances. But once you have such a physics model, and you operate in a restricted sphere within that model (308s at 1000+/- yards for example) you can get highly accurate data extraction from the well collected dataset by knowing the first order terms of the 6-DOF calculation.
{In a similar vein: once you bite on the concept that calculus describes "everyday" physics--the only difference between Newtonian Physics and any other physics is simply the constants (like 32 ft/sec/sec = Gm). Calculus itself desctibes a coupling between position, velocity, acceleration: energy, power, pressure such that you can integrate from one end or differentiate from the other. The great thing about physics is that no mater where you start, you HAVE to arrive at the same result as the same problem attacked from the other end, or you made a mistake in the calculation somewhere along the way}.
Brown Dog: I thiink we are in very good agreement--perhaps violently so.....
The difference, here, is the same as the difference between "trying to figure out what the physics is", and then "using that physics to solve a dataset".
In order to develop a full ballistics model, you must be able to do a 6-DOF calculation and fit many data points perhaps several different kinds of projectiles and distances. But once you have such a physics model, and you operate in a restricted sphere within that model (308s at 1000+/- yards for example) you can get highly accurate data extraction from the well collected dataset by knowing the first order terms of the 6-DOF calculation.
{In a similar vein: once you bite on the concept that calculus describes "everyday" physics--the only difference between Newtonian Physics and any other physics is simply the constants (like 32 ft/sec/sec = Gm). Calculus itself desctibes a coupling between position, velocity, acceleration: energy, power, pressure such that you can integrate from one end or differentiate from the other. The great thing about physics is that no mater where you start, you HAVE to arrive at the same result as the same problem attacked from the other end, or you made a mistake in the calculation somewhere along the way}.
Re: Spindrift Calculation??
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: NOBODY</div><div class="ubbcode-body">Am suprised Gain Twist hasn't been guessed at,as well. </div></div>
Ah yes, progressive rifling!
Seems the Chinese are onto that one;
Chinese 'Sniper' rifle
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: NOBODY</div><div class="ubbcode-body">Am suprised Gain Twist hasn't been guessed at,as well. </div></div>
Ah yes, progressive rifling!
Seems the Chinese are onto that one;
Chinese 'Sniper' rifle
Re: Spindrift Calculation??
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Captain Kick-Ass</div><div class="ubbcode-body">what if the Earth's magnetic poles suddenly flipped? </div></div>
Then republicans would be liberal and democrats would be conservative.....
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Captain Kick-Ass</div><div class="ubbcode-body">what if the Earth's magnetic poles suddenly flipped? </div></div>
Then republicans would be liberal and democrats would be conservative.....
Re: Spindrift Calculation??
My theory:
Most people shoot so close range that they can not see spin drift at all becaus it is so tiny. Of those who shoot long range (past 500 meters or so) only a few can actually shoot so constantly that they could notice spin drift. Of thos who can many may have their sigths canted just a little to copmensate for the drfit. I friend of mine had this happening and didn´t understand what we were talking about. Once he mounted his scope straight he become a member of our "spin drfit does exist" -cult.
Actually he is today they main priest for it
Any sniper schooled person should at some point have seen with a spotter scope how the arc of the trajectory moves the bullet (you can see the flutter and sometimes even the glitter on of sun on the bullet) even on dead calm days to the direction of the twist. Typically to the right. I can not explain that with anything else but spindrift. Could be something else but when I adjust for it I hit my targets and that is enough evidence for me.
My theory:
Most people shoot so close range that they can not see spin drift at all becaus it is so tiny. Of those who shoot long range (past 500 meters or so) only a few can actually shoot so constantly that they could notice spin drift. Of thos who can many may have their sigths canted just a little to copmensate for the drfit. I friend of mine had this happening and didn´t understand what we were talking about. Once he mounted his scope straight he become a member of our "spin drfit does exist" -cult.
Actually he is today they main priest for it Any sniper schooled person should at some point have seen with a spotter scope how the arc of the trajectory moves the bullet (you can see the flutter and sometimes even the glitter on of sun on the bullet) even on dead calm days to the direction of the twist. Typically to the right. I can not explain that with anything else but spindrift. Could be something else but when I adjust for it I hit my targets and that is enough evidence for me.
Re: Spindrift Calculation??
Wow, talk about a revelation, now we can "see" spin drift.
I'll admit it, I'm school trained, as well as spend hours a week behind a spotting scope and I can't see it, although I don't really look for it and can say, in South Texas or even in Central Colorado, North New Mexico, not to mention places like Eastern West Virginia, I have never sat through a completely wind free day, but to notice a bullet 1/3 of a inch in size drift to what equals about 1 inch at 1000 yards is incredible. Eagle eyes for sure.
I'll tell you what I have seen more than anything else on a range, people, a wide variety of people, who screw up the fundamentals of marksmanship on a regular basis. The most common error, "trigger control", which in my experience with a larger majority of right hand shooters causes the bullet to drift right... that I have seen.
Wow, talk about a revelation, now we can "see" spin drift.
I'll admit it, I'm school trained, as well as spend hours a week behind a spotting scope and I can't see it, although I don't really look for it and can say, in South Texas or even in Central Colorado, North New Mexico, not to mention places like Eastern West Virginia, I have never sat through a completely wind free day, but to notice a bullet 1/3 of a inch in size drift to what equals about 1 inch at 1000 yards is incredible. Eagle eyes for sure.
I'll tell you what I have seen more than anything else on a range, people, a wide variety of people, who screw up the fundamentals of marksmanship on a regular basis. The most common error, "trigger control", which in my experience with a larger majority of right hand shooters causes the bullet to drift right... that I have seen.
G
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Re: Spindrift Calculation??
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">
The most common error, "trigger control", which in my experience with a larger majority of right hand shooters causes the bullet to drift right... that I have seen. </div></div>
Folks in the south call that pushing wood, or fiber, which ever your shooting that day.
I'm not buying you can see a full power 30 cal flying either, but I'll bite on a left spin 1911a1 45acp, launching a 200gr swc with 3.5 grs of bullseye pushing it for sure. That I have seen with my own eyes from the 50 to 100 yds line.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">
The most common error, "trigger control", which in my experience with a larger majority of right hand shooters causes the bullet to drift right... that I have seen. </div></div>
Folks in the south call that pushing wood, or fiber, which ever your shooting that day.
I'm not buying you can see a full power 30 cal flying either, but I'll bite on a left spin 1911a1 45acp, launching a 200gr swc with 3.5 grs of bullseye pushing it for sure. That I have seen with my own eyes from the 50 to 100 yds line.
Re: Spindrift Calculation??
I just knew this thread wouldn't go away. Visual spin drift, here we go again...Honey, pop some more popcorn!
I just knew this thread wouldn't go away. Visual spin drift, here we go again...Honey, pop some more popcorn!
G
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Re: Spindrift Calculation??
Have you ever fired that combo at 50, 100yds or longer my friend? If you had and had young eyes you would see it as well.
I don't understand folks that dismiss out right, what they may have never seen, or heard of before.
Dtubb and others were right, it's a waste of time trying to explain anything here at times.
Have you ever fired that combo at 50, 100yds or longer my friend? If you had and had young eyes you would see it as well.
I don't understand folks that dismiss out right, what they may have never seen, or heard of before.
Dtubb and others were right, it's a waste of time trying to explain anything here at times.
Re: Spindrift Calculation??
First of all I have seen sun shine on .338 and 308 bullets on a good day whan using a quality spotter (mostly Swaro, sometimes Zeiss) and when shooting at long range (+800 meters). Even when the bullet can not be seen the turbulence in the air can be seen.
My 250 Scenars bullets to drift apprx. 0.3 mrad at 1000 meters. That is 12" on a bullet path that should be totally straight. No correction and I will miss. If you do not have to make corrections then lucky you.
Best place to spot the bullet flight is straight behind the shooter.
Somehow this discussion reminds me of the discussions from 3-4 years ago when I dared to tell the audience that 155 Scenar kicks ass at 1000 meters and beyond. I got laughed at "155 Sierra Palma bullet flies crappy at 1000 yards and therefore you are full of it" comments Somehow nowadays it is commonly accepted even in Snipershide that 155 Sc is a good +1000 meter bullet in a 308.
BTW did you know that the M1903 Spiringfield rifle has the rear sights milled so that that it automatically takes care of the spin dirft effect at long range ?
First of all I have seen sun shine on .338 and 308 bullets on a good day whan using a quality spotter (mostly Swaro, sometimes Zeiss) and when shooting at long range (+800 meters). Even when the bullet can not be seen the turbulence in the air can be seen.
My 250 Scenars bullets to drift apprx. 0.3 mrad at 1000 meters. That is 12" on a bullet path that should be totally straight. No correction and I will miss. If you do not have to make corrections then lucky you.
Best place to spot the bullet flight is straight behind the shooter.
Somehow this discussion reminds me of the discussions from 3-4 years ago when I dared to tell the audience that 155 Scenar kicks ass at 1000 meters and beyond. I got laughed at "155 Sierra Palma bullet flies crappy at 1000 yards and therefore you are full of it" comments
Somehow nowadays it is commonly accepted even in Snipershide that 155 Sc is a good +1000 meter bullet in a 308.BTW did you know that the M1903 Spiringfield rifle has the rear sights milled so that that it automatically takes care of the spin dirft effect at long range ?
Re: Spindrift Calculation??
It's not uncommon to see bullets glinting in the sun going down range, or seeing vapor trails as they move across the field... but to say you can see Spin Drift, again, I have to say, a revelation.
I see a lot of things through my spotter, I watched the wind blow a shot over a hill, as it was falling suddenly it climbed and impacted high. I seen bullets fired wide left impact right, again, wind... bullets aren't smart weapons they go where they are pointed until acted upon.
TA, what range is your 338 zeroed at to move 12" at 1000, 100 ? If so, that would mean in a no wind situation on an 18" wide target no one who holds dead center can possibly hit the target. That would be the absolute mathematics of it... so I suggest a blind shoot in no wind were 10 people line up and aim dead center, if everyone hits 3" off the plate then we have absolute proof of what spin drift equals at that distance. However if with a center hold at 1000 yards on an 18" target some one, or two people hit the target, we have an issue.
Maybe next time anyone, or everyone for that matter who goes to an F Class type match, after the match is over he polls the shooters and records the score of each to see if those who add for spin drift surely shoot better than those who do not.
Numbers are out there, but clearly we have an issue of those who choose not to use it verses those who do... because clearly there is not scoring statistic I know of to show it gives a user of spin drift a clear advantage.
It's not uncommon to see bullets glinting in the sun going down range, or seeing vapor trails as they move across the field... but to say you can see Spin Drift, again, I have to say, a revelation.
I see a lot of things through my spotter, I watched the wind blow a shot over a hill, as it was falling suddenly it climbed and impacted high. I seen bullets fired wide left impact right, again, wind... bullets aren't smart weapons they go where they are pointed until acted upon.
TA, what range is your 338 zeroed at to move 12" at 1000, 100 ? If so, that would mean in a no wind situation on an 18" wide target no one who holds dead center can possibly hit the target. That would be the absolute mathematics of it... so I suggest a blind shoot in no wind were 10 people line up and aim dead center, if everyone hits 3" off the plate then we have absolute proof of what spin drift equals at that distance. However if with a center hold at 1000 yards on an 18" target some one, or two people hit the target, we have an issue.
Maybe next time anyone, or everyone for that matter who goes to an F Class type match, after the match is over he polls the shooters and records the score of each to see if those who add for spin drift surely shoot better than those who do not.
Numbers are out there, but clearly we have an issue of those who choose not to use it verses those who do... because clearly there is not scoring statistic I know of to show it gives a user of spin drift a clear advantage.
Re: Spindrift Calculation??
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">I can see the world spin: it looks as if it is standing still.
</div></div>
That only works for me when I spin around real fast for a minute or so and then stop!
Can someone please explain the point of this post continuing the way it has? What is your goal, what are you trying to prove, what point are you trying to get across? Just tell us so we can be done with this!
Does spin drift exist...YES but so do black holes in the universe. Who cares!
I would guess that 99.99% of shooters adjust consciously or sub-consciously for spin drift with their windage corrections at long ranges. This is primarily because we shoot in places where there is always some type of wind blowing even if it’s a light breeze. I can’t think of a single place I've ever shoot that was ever dead calm, so spin drift doesn’t even enter into my thought process.
If you can see the difference between spin drift and wind deflection of a bullet going down range you truly have eagle eyes and you’ve been given a true gift. I have 20/20 vision, still at age 47 and I’ve watched many bullets go down range from my spotter. I would never make a statement like that…mainly because I don’t have eagle eyes and I have my doubts when I hear a statement like that! Not sure how you compensate for spin drift on a cloudy day...nor do I care.
So if it helps and this will help put this thread out of everyone’s misery, "Yes spin drift exists", and you have outstanding vision!
UNCLE I call UNCLE!
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">I can see the world spin: it looks as if it is standing still.
That only works for me when I spin around real fast for a minute or so and then stop!
Does spin drift exist...YES but so do black holes in the universe. Who cares!
I would guess that 99.99% of shooters adjust consciously or sub-consciously for spin drift with their windage corrections at long ranges. This is primarily because we shoot in places where there is always some type of wind blowing even if it’s a light breeze. I can’t think of a single place I've ever shoot that was ever dead calm, so spin drift doesn’t even enter into my thought process.
If you can see the difference between spin drift and wind deflection of a bullet going down range you truly have eagle eyes and you’ve been given a true gift. I have 20/20 vision, still at age 47 and I’ve watched many bullets go down range from my spotter. I would never make a statement like that…mainly because I don’t have eagle eyes and I have my doubts when I hear a statement like that! Not sure how you compensate for spin drift on a cloudy day...nor do I care.
So if it helps and this will help put this thread out of everyone’s misery, "Yes spin drift exists", and you have outstanding vision!
UNCLE I call UNCLE!
Re: Spindrift Calculation??
Just a podium for those educated beyond their intelligence,to prove same.
I'm thankful for the stage and appreciate the humor.
Just a podium for those educated beyond their intelligence,to prove same.
I'm thankful for the stage and appreciate the humor.
Re: Spindrift Calculation??
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mike D.</div><div class="ubbcode-body"> I usually try my best to avoid the super-geek side of shootin but this is a great example of what gets wrapped around the axle.
Chad-
Justa few thoughts. First you have no real way of determinin if your first round miss at 1000 was shooter error or spin drift. As ya have said, you have no way to determine if yur scope is canted, the reticle, the rifle, just a MK 1 eyeball. Even the most anal scope mounter relies on his eyeball to determine the set-up, n pullin the rings tight can change that settin ever so slightly.
I've got a few rounds down to 1000 yards. I have never shot a 'perfect condition'. That would be a pancake flat, no tree, no gopher hole bit of ground where 8 men spaced 100 yards apart downrange can smoke n the cloud surround their respective heads.
Now on how many first round hits anyone does at 1000. I do believe that number is a single digit percentage. Waaaay too many shooter errors to overcome. I do believe if ya asked alot of shooters they would say its readin condition they work on, not lookin for the spindrift value of a distance.
Cantin a scope-
I've seen a few do that, I heard it was because David Tubb did it once
I'm not sure how a one size fits all cant works well, but then agin I never saw the advantage of meplat cuttin. Way one follower of the cant explained it to me it was to compensate for the sling twist of prone shootin, not spin drift, but what the hey...
Anyhow, while I'm sure gettin to the bottom of spindrift is an interestin way to spend time on the computer, I think it shows the side effects of not enough rangetime. Sometimes the first order of business is seperatin the chaff from the grain.
There are a couple of guys who come to Badlands to shoot one mile. They use the 7 remmag. They didnt calculate spin drift, arguin with the wind keeps em busy enough.... </div></div>
Not going to comment on Meplat trimming perse , but you can see the modeled trajectory difference at long range by having a slightly bigger or smaller meplat diameter on the same bullet only difference is the meplat diameter and nose length because of the diameter change.
When you model the two bullets with all other parameters equal there can be quite a few inches difference at say 1000 yards.
Closing the meplat and making it neater and straighter accross the axis of the bullet does show a flatter trajectory at extended range modeled in ballistic software. How well that translates to more accuracy at extended range compared to not doing it I can't tell as I make my own and they don't need trimming or closing .
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mike D.</div><div class="ubbcode-body"> I usually try my best to avoid the super-geek side of shootin but this is a great example of what gets wrapped around the axle.
Chad-
Justa few thoughts. First you have no real way of determinin if your first round miss at 1000 was shooter error or spin drift. As ya have said, you have no way to determine if yur scope is canted, the reticle, the rifle, just a MK 1 eyeball. Even the most anal scope mounter relies on his eyeball to determine the set-up, n pullin the rings tight can change that settin ever so slightly.
I've got a few rounds down to 1000 yards. I have never shot a 'perfect condition'. That would be a pancake flat, no tree, no gopher hole bit of ground where 8 men spaced 100 yards apart downrange can smoke n the cloud surround their respective heads.
Now on how many first round hits anyone does at 1000. I do believe that number is a single digit percentage. Waaaay too many shooter errors to overcome. I do believe if ya asked alot of shooters they would say its readin condition they work on, not lookin for the spindrift value of a distance.
Cantin a scope-
I've seen a few do that, I heard it was because David Tubb did it once
Anyhow, while I'm sure gettin to the bottom of spindrift is an interestin way to spend time on the computer, I think it shows the side effects of not enough rangetime. Sometimes the first order of business is seperatin the chaff from the grain.
There are a couple of guys who come to Badlands to shoot one mile. They use the 7 remmag. They didnt calculate spin drift, arguin with the wind keeps em busy enough.... </div></div>
Not going to comment on Meplat trimming perse , but you can see the modeled trajectory difference at long range by having a slightly bigger or smaller meplat diameter on the same bullet only difference is the meplat diameter and nose length because of the diameter change.
When you model the two bullets with all other parameters equal there can be quite a few inches difference at say 1000 yards.
Closing the meplat and making it neater and straighter accross the axis of the bullet does show a flatter trajectory at extended range modeled in ballistic software. How well that translates to more accuracy at extended range compared to not doing it I can't tell as I make my own and they don't need trimming or closing .
Re: Spindrift Calculation??
The drift with my 338LM is at 1000 meters 1 MOA i.e. 12 inches or 29cm. That with a windage zeroed at 300m on a calm day. BTW 1000 meters is 1094 yards. I am not really talking about 700 or 900 yards. The matter is getting serious past 1000 yards.
I can not explain the 7WSM 1997 yards no sd correction by anything else than misjudged wind that compensated for the drift. I HAVE shot with zero windage to 1000 and 1100 meters a few times when the side wind from right to left compensated FULLY for the SD. More often I have to adjust for SD at those ranges.
Enough of this for my part. If someone does not believe in SD that is fine with me.
The drift with my 338LM is at 1000 meters 1 MOA i.e. 12 inches or 29cm. That with a windage zeroed at 300m on a calm day. BTW 1000 meters is 1094 yards. I am not really talking about 700 or 900 yards. The matter is getting serious past 1000 yards.
I can not explain the 7WSM 1997 yards no sd correction by anything else than misjudged wind that compensated for the drift. I HAVE shot with zero windage to 1000 and 1100 meters a few times when the side wind from right to left compensated FULLY for the SD. More often I have to adjust for SD at those ranges.
Enough of this for my part. If someone does not believe in SD that is fine with me.
Re: Spindrift Calculation??
The spindrift of a bullet fired mostly parallel to the earth is (within reason) completely and solely a matter of time-of-flight. It's not the bullet that turns, it's the Earth below it.
I know I sound a lot like a one-trick-pony these days (there he goes again, Ole TOF Greg...), but really folks; quite a lot of what we do is governed by that single, simple factor.
As I said somewhere else today, it's easy to imagine lots of other factors. But like most things imaginary, explaining them becomes rather difficult when force diagrams, equations with real numbers, and solid evidence are the price of admission to the cardgame.
Greg
The spindrift of a bullet fired mostly parallel to the earth is (within reason) completely and solely a matter of time-of-flight. It's not the bullet that turns, it's the Earth below it.
I know I sound a lot like a one-trick-pony these days (there he goes again, Ole TOF Greg...), but really folks; quite a lot of what we do is governed by that single, simple factor.
As I said somewhere else today, it's easy to imagine lots of other factors. But like most things imaginary, explaining them becomes rather difficult when force diagrams, equations with real numbers, and solid evidence are the price of admission to the cardgame.
Greg
Re: Spindrift Calculation??
Greg, that's not true about spin drift. There are TWO horizontal deviations not counting wind.
SPIN DRIFT: Is an a horizontal error due to a difference in air pressure to the right side (as you look at the projo from the rear while in flight, in a right twist gun barrel), and below the projectile, rougly from 1 o'clock to 7 o'clock. The projo "drifts" in the direction of lower air pressure. It is not a function of time of flight. It may appear to be a funtion of time because the greater the flight time, the greater the drift, but it's actually a spinning projectile thing, barrel twist rate, "K factor", projectile composition and weight are other components of the formula.
SPIN OF THE EART (CORIOLIS): This is the factor that has to do with the spin of the planet. It is dependant on 3 events. Roughly speaking, a .50 cal military round will drift 16" at 2000 yards, SAC, at 41 degrees N latitude, point the gun True north. As you swing the gun more towards east or west, the error becomes partly a range error (very small amount), and less of a windage error.
1. Time of flight.
2. Direction of the shot relative to T north.
3. Distance from the equator, the farther away from the equator, the greater the error will be.
Air temperature also affects the spin drift error, but does NOT affect the coriolis error.
Just a thought, good to be back from the land of the lost so to speak.
Trigger
Greg, that's not true about spin drift. There are TWO horizontal deviations not counting wind.
SPIN DRIFT: Is an a horizontal error due to a difference in air pressure to the right side (as you look at the projo from the rear while in flight, in a right twist gun barrel), and below the projectile, rougly from 1 o'clock to 7 o'clock. The projo "drifts" in the direction of lower air pressure. It is not a function of time of flight. It may appear to be a funtion of time because the greater the flight time, the greater the drift, but it's actually a spinning projectile thing, barrel twist rate, "K factor", projectile composition and weight are other components of the formula.
SPIN OF THE EART (CORIOLIS): This is the factor that has to do with the spin of the planet. It is dependant on 3 events. Roughly speaking, a .50 cal military round will drift 16" at 2000 yards, SAC, at 41 degrees N latitude, point the gun True north. As you swing the gun more towards east or west, the error becomes partly a range error (very small amount), and less of a windage error.
1. Time of flight.
2. Direction of the shot relative to T north.
3. Distance from the equator, the farther away from the equator, the greater the error will be.
Air temperature also affects the spin drift error, but does NOT affect the coriolis error.
Just a thought, good to be back from the land of the lost so to speak.
Trigger
Re: Spindrift Calculation??
Two Shoes,,, thanks for the kind words. Here's one for the spin drift theory...
If spin drift doesn't exist in relation to bullets in flight... airplanes wouldn't get off of the ground
Glad they do.
Trigger
Two Shoes,,, thanks for the kind words. Here's one for the spin drift theory...
If spin drift doesn't exist in relation to bullets in flight... airplanes wouldn't get off of the ground
Glad they do.
Trigger
Re: Spindrift Calculation??
Trigs;
Of course you're right. I was confusing Spindrift with Coriolis. Easy for me to do as I give neither great credence at the distances I'm shooting; they tend to fade into the 'background white noise...' in my shooting scenarios.
But I think it's also reasonable to say that whatever the mechanism(s) behind spindrift, that its amplitude is also largely governed by TOF.
Greg
Trigs;
Of course you're right. I was confusing Spindrift with Coriolis. Easy for me to do as I give neither great credence at the distances I'm shooting; they tend to fade into the 'background white noise...' in my shooting scenarios.
But I think it's also reasonable to say that whatever the mechanism(s) behind spindrift, that its amplitude is also largely governed by TOF.
Greg
Re: Spindrift Calculation??
I like the <span style="font-style: italic">"all or nothing"</span> tone, where no one has said spin drift <span style="font-weight: bold">doesn't exist</span>, but that is the ultimate interpretation to address the 'noise" issue.
When discussing 1100 yards it instantly becomes about 2000m so you don't have to admit just how small it really is and the fact more people have a problem with the fundamentals of marksmanship than any amount of "drift' caused by zero external forces on the bullet... not to mention just how hard it is to find a place to shoot where there are zero external effects.
I like the <span style="font-style: italic">"all or nothing"</span> tone, where no one has said spin drift <span style="font-weight: bold">doesn't exist</span>, but that is the ultimate interpretation to address the 'noise" issue.
When discussing 1100 yards it instantly becomes about 2000m so you don't have to admit just how small it really is and the fact more people have a problem with the fundamentals of marksmanship than any amount of "drift' caused by zero external forces on the bullet... not to mention just how hard it is to find a place to shoot where there are zero external effects.
Re: Spindrift Calculation??
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">SOTIC has taught this since the 80s and it is simply a part of the sniper/observer dialogue. Obsersver gives the shooter his elevation, spindrift and parallex all in a simple command. "Elevation 650, spin 1 left, parallax 2d ball."
Is 1 moa big at 1000 no, but if you are off 1 moa in a wind call (a 7.62mm at 1000 is thrown off by about 1.2 moa every 1 mph so this is very easy to do ) and you are off 1 moa in your spin, then you are now 2 moa off and you are screwed. At 1000 meters that is 29.2 cm and that is 11.5 inches. Twice that is 23 inches and that is a miss on a standrad sized human. Hell, that is is 11.5 inches at 600 and that is a miss or a wound at 600. Again I ask, if everyone just has to have .25 moa scopes, which I think is a waste of time, then why are you ignoring a full 1 moa or even a .5 moa in spin?
Spin of the earth has jack to do with this. It is a measurable problem with bullets and it is constant. My .50 cal black powder spins right 6 iches at 100 yards. I know this and compenstae for it at 100. The British Enfield 303 WWI shot 1 moa every 100 yards right and the troops were taught to compensate. The larger and the slower the bullet the more the drift occurs. It is caused by a combination of the cushion of air building up under a right spinning bullet and the nose of the bullet pointing into the spin and acting as a sail. Yes that is simplified but essentially what is happening.
</div></div>
I also have issue with spin drift and it is about 30cm at 1km (1MOA) shooting 175gr out of 308Win. Some believe that spin at 1km is not significant some, like me, say it is. Use whatever works for you and stick with it.
thunder11
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">SOTIC has taught this since the 80s and it is simply a part of the sniper/observer dialogue. Obsersver gives the shooter his elevation, spindrift and parallex all in a simple command. "Elevation 650, spin 1 left, parallax 2d ball."
Is 1 moa big at 1000 no, but if you are off 1 moa in a wind call (a 7.62mm at 1000 is thrown off by about 1.2 moa every 1 mph so this is very easy to do ) and you are off 1 moa in your spin, then you are now 2 moa off and you are screwed. At 1000 meters that is 29.2 cm and that is 11.5 inches. Twice that is 23 inches and that is a miss on a standrad sized human. Hell, that is is 11.5 inches at 600 and that is a miss or a wound at 600. Again I ask, if everyone just has to have .25 moa scopes, which I think is a waste of time, then why are you ignoring a full 1 moa or even a .5 moa in spin?
Spin of the earth has jack to do with this. It is a measurable problem with bullets and it is constant. My .50 cal black powder spins right 6 iches at 100 yards. I know this and compenstae for it at 100. The British Enfield 303 WWI shot 1 moa every 100 yards right and the troops were taught to compensate. The larger and the slower the bullet the more the drift occurs. It is caused by a combination of the cushion of air building up under a right spinning bullet and the nose of the bullet pointing into the spin and acting as a sail. Yes that is simplified but essentially what is happening.
</div></div>
I also have issue with spin drift and it is about 30cm at 1km (1MOA) shooting 175gr out of 308Win. Some believe that spin at 1km is not significant some, like me, say it is. Use whatever works for you and stick with it.
thunder11
Re: Spindrift Calculation??
Someone needs to post a wind table then that accounts for spin drift inside a 1100 yards as it is growing in size again.
Cause if everyone and their brother is 'not" using it, even in wind, then there is a whole lot more missing going on even in the wind.
30cm / 1 MOA on a 18" wide target with a center hold is a miss... wind or not. I know I personally shoot smaller targets than that without it, so my misses should be more frequent and larger by a fair margin.
Personally I think the number has been rounded up so many times it's now 3X it's actual size.
Someone needs to post a wind table then that accounts for spin drift inside a 1100 yards as it is growing in size again.
Cause if everyone and their brother is 'not" using it, even in wind, then there is a whole lot more missing going on even in the wind.
30cm / 1 MOA on a 18" wide target with a center hold is a miss... wind or not. I know I personally shoot smaller targets than that without it, so my misses should be more frequent and larger by a fair margin.
Personally I think the number has been rounded up so many times it's now 3X it's actual size.
Re: Spindrift Calculation??
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Someone needs to post a wind table then that accounts for spin drift inside a 1100 yards </div></div>
errr.....
<span style="font-weight: bold">I did</span>
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Brown Dog</div><div class="ubbcode-body">155 Scenar at 2940fps 1:12 twist average conditions for where I live:
(Spin) Drift Corrections:
</div></div>
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Brown Dog</div><div class="ubbcode-body">The table is in metres and <span style="font-weight: bold">0.1mRad </span>clicks (which I would normally round to the nearest whole click)
so, at 1000<span style="font-weight: bold">m </span>the chart is showing 0.36mils ..around 14 inches
at 910m (1000yds give or take) it's showing 0.3mils ...around 10.75 inches </div></div>
To use it; simply calculate deflection then apply drift
More or less the methodology described in the SOTIC quote....
It ain't rocket science
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Someone needs to post a wind table then that accounts for spin drift inside a 1100 yards </div></div>
errr.....
<span style="font-weight: bold">I did</span>
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Brown Dog</div><div class="ubbcode-body">155 Scenar at 2940fps 1:12 twist average conditions for where I live:
(Spin) Drift Corrections:
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Brown Dog</div><div class="ubbcode-body">The table is in metres and <span style="font-weight: bold">0.1mRad </span>clicks (which I would normally round to the nearest whole click)
so, at 1000<span style="font-weight: bold">m </span>the chart is showing 0.36mils ..around 14 inches
at 910m (1000yds give or take) it's showing 0.3mils ...around 10.75 inches </div></div>
To use it; simply calculate deflection then apply drift
More or less the methodology described in the SOTIC quote....
It ain't rocket science
Re: Spindrift Calculation??
No it ain't rocket science and 3 tenths mill adjustment for sprin dirift at 1K is a miss on the 10 inch wide target that I shoot. If you get 10.75 inches of spin drift with a 155 bullet then you are an unlucky individual. I am solidly with LowLight on this one..
No it ain't rocket science and 3 tenths mill adjustment for sprin dirift at 1K is a miss on the 10 inch wide target that I shoot. If you get 10.75 inches of spin drift with a 155 bullet then you are an unlucky individual. I am solidly with LowLight on this one..
Re: Spindrift Calculation??
What you posted is not what I mean, that is your figures for spin drift made in a separate chart.
The chart would be a combination of wind and Spin drift as your numbers as well as other proponents of SD show 1 MOA or so at 1k... well combined with wind that is a big deal.
here is what I did.
I just ran the wind using a 175gr going 2600fps out to 1100 yards.
I used, Patagonia, Nightforce Exbal, JBM and Horus... I also changed the direction of the wind from 3 O'clock to 9 O'Clock so I can see if there is a difference.
What I got was:
JBM = 127.3 from either direction with a correction of 3.2 mils
Horus ATRAG = 3.24 Mils correct regardless of the direction
Exbal = 127 inches of drift regardless of the direction with 3.2 Mils of correction or 11 MOA.
Patagonia = 137.7 inches of drift with a 3.5 Mils of hold.
So a lot of people are getting bad information cause they are all missing their targets in one direction or another.
No one who uses any published wind chart should be able to hit anything at 1000 yards because even with the wind correction they should be missing an 18" or smaller target each time they pull the trigger... the math you posted can't lie... 10.75", even with wind dialed in on a center hold is a miss by 1.75" each and every time thanks to SD.
What you posted is not what I mean, that is your figures for spin drift made in a separate chart.
The chart would be a combination of wind and Spin drift as your numbers as well as other proponents of SD show 1 MOA or so at 1k... well combined with wind that is a big deal.
here is what I did.
I just ran the wind using a 175gr going 2600fps out to 1100 yards.
I used, Patagonia, Nightforce Exbal, JBM and Horus... I also changed the direction of the wind from 3 O'clock to 9 O'Clock so I can see if there is a difference.
What I got was:
JBM = 127.3 from either direction with a correction of 3.2 mils
Horus ATRAG = 3.24 Mils correct regardless of the direction
Exbal = 127 inches of drift regardless of the direction with 3.2 Mils of correction or 11 MOA.
Patagonia = 137.7 inches of drift with a 3.5 Mils of hold.
So a lot of people are getting bad information cause they are all missing their targets in one direction or another.
No one who uses any published wind chart should be able to hit anything at 1000 yards because even with the wind correction they should be missing an 18" or smaller target each time they pull the trigger... the math you posted can't lie... 10.75", even with wind dialed in on a center hold is a miss by 1.75" each and every time thanks to SD.
Re: Spindrift Calculation??
That has been my contention from the start spin drift is not calculateable before hand if one is shooting a bullet that exhibits a noticable amount of spin drift, it must be shot to determine the amount that needs to be accounted for. Exbal has a spot for the measured amount of spin drift to be entered and then it will acount for it. All bullets are not worth worrying about as can be demonstrated simply by shooting them down range on a regular basis
That has been my contention from the start spin drift is not calculateable before hand if one is shooting a bullet that exhibits a noticable amount of spin drift, it must be shot to determine the amount that needs to be accounted for. Exbal has a spot for the measured amount of spin drift to be entered and then it will acount for it. All bullets are not worth worrying about as can be demonstrated simply by shooting them down range on a regular basis
Re: Spindrift Calculation??
Frank, why don't you call the makers of the programs?
They will all tell you what Brown Dog and I have been trying to explain. There is an aprox. 1.0 MOA of SD with this load, some take it into account and some don't. Even the really old militry manuals show this drift, and this was based on shooting tests. No hand held program really calculates it but they have a simplified method/guesstimation based on tests of similar bullets.
Remember that SD is very small at short ranges, in the above example by Brown Dog it is only about 0.4 MOA at 600 yds (550 m), very difficult to notice. And it is difficult to be certain of the exact amount of SD at 1000 yds since nobody knows what the wind is really doing downrange, but when you have a 1.0 error it is significant in my book and worth considering.
Also remember that while ALL rifle/loads have significant SD at long range, this is not only masked by the wind but can also be somewhat/totally offset by small canting or turret errors and in this case the individual gun can be apparently SD free at long range. Small canting or turret errors are also very difficult to notice at short ranges since the error is proportional to the elevation that is dialed into the scope, so while the scope may be apparently tracking perfectly at short ranges the error will show at long range.
So if you want to start correcting for small errors like 1.0 MOA at 1000 yds you better be shure the scope is tracking perfectly: align the reticle to a vertical line at 100 yds and dial up 40 MOA or so, see if it still in the same vertical line. And you need to be shure you are not canting the gun, just a small angle will show in the horizontal POI at long range.
Frank, why don't you call the makers of the programs?
They will all tell you what Brown Dog and I have been trying to explain. There is an aprox. 1.0 MOA of SD with this load, some take it into account and some don't. Even the really old militry manuals show this drift, and this was based on shooting tests. No hand held program really calculates it but they have a simplified method/guesstimation based on tests of similar bullets.
Remember that SD is very small at short ranges, in the above example by Brown Dog it is only about 0.4 MOA at 600 yds (550 m), very difficult to notice. And it is difficult to be certain of the exact amount of SD at 1000 yds since nobody knows what the wind is really doing downrange, but when you have a 1.0 error it is significant in my book and worth considering.
Also remember that while ALL rifle/loads have significant SD at long range, this is not only masked by the wind but can also be somewhat/totally offset by small canting or turret errors and in this case the individual gun can be apparently SD free at long range. Small canting or turret errors are also very difficult to notice at short ranges since the error is proportional to the elevation that is dialed into the scope, so while the scope may be apparently tracking perfectly at short ranges the error will show at long range.
So if you want to start correcting for small errors like 1.0 MOA at 1000 yds you better be shure the scope is tracking perfectly: align the reticle to a vertical line at 100 yds and dial up 40 MOA or so, see if it still in the same vertical line. And you need to be shure you are not canting the gun, just a small angle will show in the horizontal POI at long range.
Re: Spindrift Calculation??
That's what I have been saying, when you consider all the possibilities... it's noise.
That's what I have been saying, when you consider all the possibilities... it's noise.
Re: Spindrift Calculation??
Oh, and PS, just to prove a point, here is a page from a "military" manual if you feel quoting them is worth the time:
Just because the military said it, doesn't make it right, and unscientific numbers from people who could have well been pulling the trigger wrong doesn't make it fact.
Oh, and PS, just to prove a point, here is a page from a "military" manual if you feel quoting them is worth the time:
Just because the military said it, doesn't make it right, and unscientific numbers from people who could have well been pulling the trigger wrong doesn't make it fact.
Re: Spindrift Calculation??
LL, good cath and not the only one
The military manuals I mentioned had data based on very extensive shooting under the "low tech lab" conditions of the era, mainly used to establish the BC of the bullet. And it matches all currents test data too.
In my opinion, once you get close to 1.0 MOA the error is worth considering. And lost in the noise depends on your style of shooting and your target size, in truth for my shooting style there are MANY things losts in the noise and taken care of in the second shot. But for someone who has a level, time to set up for a shot, and wants that first bullet as close as possible to the target (...always at the mercy of the wind gods) it may be worth it. In summary, and depending on your equipment and shooting style:
short/medium range (up to 6-700 yds?) = disregard
"normal" long range (700 to 1100 yds) = grey zone, your call
very/ultra long range (1100+ yds) = take into account
LL, good cath and not the only one
The military manuals I mentioned had data based on very extensive shooting under the "low tech lab" conditions of the era, mainly used to establish the BC of the bullet. And it matches all currents test data too.
In my opinion, once you get close to 1.0 MOA the error is worth considering. And lost in the noise depends on your style of shooting and your target size, in truth for my shooting style there are MANY things losts in the noise and taken care of in the second shot. But for someone who has a level, time to set up for a shot, and wants that first bullet as close as possible to the target (...always at the mercy of the wind gods) it may be worth it. In summary, and depending on your equipment and shooting style:
short/medium range (up to 6-700 yds?) = disregard
"normal" long range (700 to 1100 yds) = grey zone, your call
very/ultra long range (1100+ yds) = take into account
Re: Spindrift Calculation??
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: thunder11</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">SOTIC has taught this since the 80s and it is simply a part of the sniper/observer dialogue. Obsersver gives the shooter his elevation, spindrift and parallex all in a simple command. "Elevation 650, spin 1 left, parallax 2d ball."
Is 1 moa big at 1000 no, but if you are off 1 moa in a wind call (a 7.62mm at 1000 is thrown off by about 1.2 moa every 1 mph so this is very easy to do ) and you are off 1 moa in your spin, then you are now 2 moa off and you are screwed. At 1000 meters that is 29.2 cm and that is 11.5 inches. Twice that is 23 inches and that is a miss on a standrad sized human. Hell, that is is 11.5 inches at 600 and that is a miss or a wound at 600. Again I ask, if everyone just has to have .25 moa scopes, which I think is a waste of time, then why are you ignoring a full 1 moa or even a .5 moa in spin?
Spin of the earth has jack to do with this. It is a measurable problem with bullets and it is constant. My .50 cal black powder spins right 6 iches at 100 yards. I know this and compenstae for it at 100. The British Enfield 303 WWI shot 1 moa every 100 yards right and the troops were taught to compensate. The larger and the slower the bullet the more the drift occurs. It is caused by a combination of the cushion of air building up under a right spinning bullet and the nose of the bullet pointing into the spin and acting as a sail. Yes that is simplified but essentially what is happening.
</div></div>
I also have issue with spin drift and it is about 30cm at 1km (1MOA) shooting 175gr out of 308Win. Some believe that spin at 1km is not significant some, like me, say it is. Use whatever works for you and stick with it.
thunder11 </div></div>
Not to beat my chest, but I introduced spin drift corrections at SOTIC in 1989. 1st class taught was late summer of 1989. It was a manual calculation that I worked up while developing the .50 cal. tables that I still use to this day. It was done some very very dated (1917) Naval gunnery texts and some modifications to the formula, then compared against data from APG with some baseline projectiles to verify the accuracy of the calculations (i.e. derived K factor values, projectile specific gravity, etc).
At first, there was huge resistance to this correction because it wasn't taught anywhere else including SOTIC before this time. In informal survey of other schools (USMC Scout Sniper school at Quantico, Camp Lejeune's staff, Ft. Bennings AMU, and Cpt. R.J. Thomas of the Navy's rifle team), verified observations from long range shooting. It took a LONG time to get the spin drift langauge into the class materials. It wasn't mentioned in the SOTIC Special Operations Sniping Manual that came out around 92, because the powers that reviewed the field notes from the various SF units didn't take corrections into consideration. The first draft became the produced manual, and is hence, WEAK.
Just some history...
Trigger
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: thunder11</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">SOTIC has taught this since the 80s and it is simply a part of the sniper/observer dialogue. Obsersver gives the shooter his elevation, spindrift and parallex all in a simple command. "Elevation 650, spin 1 left, parallax 2d ball."
Is 1 moa big at 1000 no, but if you are off 1 moa in a wind call (a 7.62mm at 1000 is thrown off by about 1.2 moa every 1 mph so this is very easy to do ) and you are off 1 moa in your spin, then you are now 2 moa off and you are screwed. At 1000 meters that is 29.2 cm and that is 11.5 inches. Twice that is 23 inches and that is a miss on a standrad sized human. Hell, that is is 11.5 inches at 600 and that is a miss or a wound at 600. Again I ask, if everyone just has to have .25 moa scopes, which I think is a waste of time, then why are you ignoring a full 1 moa or even a .5 moa in spin?
Spin of the earth has jack to do with this. It is a measurable problem with bullets and it is constant. My .50 cal black powder spins right 6 iches at 100 yards. I know this and compenstae for it at 100. The British Enfield 303 WWI shot 1 moa every 100 yards right and the troops were taught to compensate. The larger and the slower the bullet the more the drift occurs. It is caused by a combination of the cushion of air building up under a right spinning bullet and the nose of the bullet pointing into the spin and acting as a sail. Yes that is simplified but essentially what is happening.
</div></div>
I also have issue with spin drift and it is about 30cm at 1km (1MOA) shooting 175gr out of 308Win. Some believe that spin at 1km is not significant some, like me, say it is. Use whatever works for you and stick with it.
thunder11 </div></div>
Not to beat my chest, but I introduced spin drift corrections at SOTIC in 1989. 1st class taught was late summer of 1989. It was a manual calculation that I worked up while developing the .50 cal. tables that I still use to this day. It was done some very very dated (1917) Naval gunnery texts and some modifications to the formula, then compared against data from APG with some baseline projectiles to verify the accuracy of the calculations (i.e. derived K factor values, projectile specific gravity, etc).
At first, there was huge resistance to this correction because it wasn't taught anywhere else including SOTIC before this time. In informal survey of other schools (USMC Scout Sniper school at Quantico, Camp Lejeune's staff, Ft. Bennings AMU, and Cpt. R.J. Thomas of the Navy's rifle team), verified observations from long range shooting. It took a LONG time to get the spin drift langauge into the class materials. It wasn't mentioned in the SOTIC Special Operations Sniping Manual that came out around 92, because the powers that reviewed the field notes from the various SF units didn't take corrections into consideration. The first draft became the produced manual, and is hence, WEAK.
Just some history...
Trigger
Re: Spindrift Calculation??
At the end of the day it’s all a mute point. Unless you shoot in a truly windless environment or where the wind blows at a constant speed and direction across the entire bullet path you cannot accurately calculate spin drift! After all of this discussion you’ll still compensate for spindrift in your windage adjustment. Practice, accurate and up to date log books and sending lots of bullets down line will give you accurate data on how your bullet performs. With this you’ll also have the necessary information for adjustments needed to hit your intended target at long ranges. Factored into all those adjustments will be corrections for spin drift whether or not they were intentional spin drift corrections or not.
As I’ve stated spin drift exists but is one of those intangible factors that is just too difficult to accurately calculate and/or predict given all of the other variables of shooting at very long ranges.
At the end of the day it’s all a mute point. Unless you shoot in a truly windless environment or where the wind blows at a constant speed and direction across the entire bullet path you cannot accurately calculate spin drift! After all of this discussion you’ll still compensate for spindrift in your windage adjustment. Practice, accurate and up to date log books and sending lots of bullets down line will give you accurate data on how your bullet performs. With this you’ll also have the necessary information for adjustments needed to hit your intended target at long ranges. Factored into all those adjustments will be corrections for spin drift whether or not they were intentional spin drift corrections or not.
As I’ve stated spin drift exists but is one of those intangible factors that is just too difficult to accurately calculate and/or predict given all of the other variables of shooting at very long ranges.
Re: Spindrift Calculation??
Allow me to explain the reason for addressing spin drift another way...
You have 7 components of horizontal possible error:
1. Wind drift.
2. Spin Drift
3. Coriolis
4. Air temp effects on 1 and 2
5. BP effects on 1 and 2
6. Projectile stability error on all of them.
7. SHOOTER induced error on all of them.
Consider that you can only do something about 1, 2, 3, 4, and 6. Less so on 4 and 6. We agree that you don't shoot to a POINT of attack on any target, you shoot to a circular error of probability. For the sake of discussion, say this CEP is 10" (generous number) at 1000 yards.
A shooter is not correcting his sights to put the "desired point of impact" on the center of the target, but the shooter is desiring to keep that 10" circle in the center of the target. On a 1000 yd bull, that's the entire diameter of the X ring, which out of 20 shots is the max number most shooters go for, last record I am aware of is a perfect 200 score with 18 Xs? SO, keeping in mind that the 10" circle in the center of the tareget is the goal, OR, your bullet might strike along the side of that 10" error CEP.
By allowing "slop" to enter the formula, or ignoring errors that you CAN correct for, you simply give away more than half of that 10" CEP. For a 175 gr. SMK out of the M-24, the spin drift is 11.43" measured by Doppler in 2001. By ignoring the first component of horizontal error, the shooter is "Giving away" half of his ability to "center up the shot".
NOW, combine this error, with a error in assessing the wind downrange in the direction of drift (left to right), you now, are allowing yourself even LESS error in determining the wind. Don't take this wrong, BUT, i've seen years and years of using HISTORICAL data not DETERMINING data used to make long range shots, and the historical data falls down nearly every time. Historical data cannot account for air conditions in my experience, unless you are talking match shooters that shoot a circuit that is roughly the same time of the year and rarely do those shots reach into the near subsonic range. Even at 1000 yards, competitors are using guns that go supersonic for another 300-500 yards typically.
The guys that shoot 1000 yards with 308 guns, Palma guys, see the minute error effects of ignoring those conditions. Mr. Art Sievers, who coached the 1969 Palma gold medal team definately addressed spin drift, he didn't know it was that, but he knew that in a no wind condition, he would put "x" MOA on his rifle team's sights at 800, 900 and 1000 yards. I'm a perfectionist, I don't and won't ignore any factor that can be accounted for or corrected for.
I'd suggest that if these small things are ignorable, the situation isn't reaching into the last 10% of the gun's supersonic range. But then again, that's why alot of competitors us technology, hotrod guns, hotrod bullets ,etc. to give them the edge and the ability to ignore the 2% conditions that cause misses and 10s instead of Xs.
Humbly,
Trigger
ps.. in the following video, without 2.00 MOA of left drift, this 25" wide target would have been MISSED.
MK 211 STRIKE FROM 1560 METERS... SPIN DRIFT INCLUDED, NO WIND
Allow me to explain the reason for addressing spin drift another way...
You have 7 components of horizontal possible error:
1. Wind drift.
2. Spin Drift
3. Coriolis
4. Air temp effects on 1 and 2
5. BP effects on 1 and 2
6. Projectile stability error on all of them.
7. SHOOTER induced error on all of them.
Consider that you can only do something about 1, 2, 3, 4, and 6. Less so on 4 and 6. We agree that you don't shoot to a POINT of attack on any target, you shoot to a circular error of probability. For the sake of discussion, say this CEP is 10" (generous number) at 1000 yards.
A shooter is not correcting his sights to put the "desired point of impact" on the center of the target, but the shooter is desiring to keep that 10" circle in the center of the target. On a 1000 yd bull, that's the entire diameter of the X ring, which out of 20 shots is the max number most shooters go for, last record I am aware of is a perfect 200 score with 18 Xs? SO, keeping in mind that the 10" circle in the center of the tareget is the goal, OR, your bullet might strike along the side of that 10" error CEP.
By allowing "slop" to enter the formula, or ignoring errors that you CAN correct for, you simply give away more than half of that 10" CEP. For a 175 gr. SMK out of the M-24, the spin drift is 11.43" measured by Doppler in 2001. By ignoring the first component of horizontal error, the shooter is "Giving away" half of his ability to "center up the shot".
NOW, combine this error, with a error in assessing the wind downrange in the direction of drift (left to right), you now, are allowing yourself even LESS error in determining the wind. Don't take this wrong, BUT, i've seen years and years of using HISTORICAL data not DETERMINING data used to make long range shots, and the historical data falls down nearly every time. Historical data cannot account for air conditions in my experience, unless you are talking match shooters that shoot a circuit that is roughly the same time of the year and rarely do those shots reach into the near subsonic range. Even at 1000 yards, competitors are using guns that go supersonic for another 300-500 yards typically.
The guys that shoot 1000 yards with 308 guns, Palma guys, see the minute error effects of ignoring those conditions. Mr. Art Sievers, who coached the 1969 Palma gold medal team definately addressed spin drift, he didn't know it was that, but he knew that in a no wind condition, he would put "x" MOA on his rifle team's sights at 800, 900 and 1000 yards. I'm a perfectionist, I don't and won't ignore any factor that can be accounted for or corrected for.
I'd suggest that if these small things are ignorable, the situation isn't reaching into the last 10% of the gun's supersonic range. But then again, that's why alot of competitors us technology, hotrod guns, hotrod bullets ,etc. to give them the edge and the ability to ignore the 2% conditions that cause misses and 10s instead of Xs.
Humbly,
Trigger
ps.. in the following video, without 2.00 MOA of left drift, this 25" wide target would have been MISSED.
MK 211 STRIKE FROM 1560 METERS... SPIN DRIFT INCLUDED, NO WIND
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