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Range Report Spindrift Calculation??

ChadTRG42

ChadTRG42

Gunny Sergeant
Full Member
Minuteman
Jan 22, 2007
3,338
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Dallas, Texas
www.dallasreloads.com
Are there internet sites or free programs that will calculate spindrift for a given bullet/rifle set-up? I am searching but not finding anything.
Trying to calculate for a 300 WM shooting a 190 SMK at 3075 fps with a 1:11" right hand twist.
Thanks!

Chad
 
Re: Spindrift Calculation??

I can't easily give you every range progression but with your combo and my weather (85 deg, 28.10 baro)

500 yards-.19moa
1000 yards-.55 moa
1500 yards- 1.27 moa

Per Cheytac ABC
 
Re: Spindrift Calculation??

Later, thanks, I thought that was usable only if you bought the program?.
 
Re: Spindrift Calculation??

I actually downloaded the trial version of Precision Shooter's Workbench yesterday. It takes a little bit to set up. The results do not follow my field elevations like some other programs do. It takes me 23.5 MOA to 1000, and it says 25.2 MOA. But, it could be me just not having all the proper fields filled in, or the program using different drag functions and such. I am not familiar enough with it to know the ins and outs yet.

http://www.precisionworkbench.com/
 
Re: Spindrift Calculation??

There is a simple answer to spin drift, its called a ZERO. People sure seem to complacate shooting.

Seeing the lack of cleaned 1000 yard targets (with about a 2 min 10-X ring), I think spindrift is the last thing we need to worry about.

No computer, calculators, fomulars, sliderules, Bal. Programs, etc can beat rounds down range.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChadTRG42</div><div class="ubbcode-body">Are there internet sites or free programs that will calculate spindrift for a given bullet/rifle set-up? I am searching but not finding anything.
Trying to calculate for a 300 WM shooting a 190 SMK at 3075 fps with a 1:11" right hand twist.
Thanks!

Chad
</div></div>

All bullets do not exhibit spin drift and I dought the 190 SMK will exhibit any spin drift. Very long extremely high VLD or ULD bullet can exhibit spin drift.
The only way to is to shoot a group at 600 yards on a calm clear morning before the sun is up andglaring, measure the center of your group to the center of your aim point and that is your amount of spin drift. The Exball ballistics targeting soft warew has a spot to enter your amount of spin drift.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jwp475</div><div class="ubbcode-body"> All bullets do not exhibit spin drift and I dought the 190 SMK will exhibit any spin drift. Very long extremely high VLD or ULD bullet can exhibit spin drift.
</div></div>

Are you for real? I suppose that radar range at Yuma is just useless and provides wrong data generated even though they have cameras and sensors every 25yards. Maybe someone should tell the bullet manufactures, ballistic program writers, etc that they are wasting that 25K per day to shoot thousands and thousands of bullets at the range to gather true downfield data.

The deal with spin drift is very few people have the capabilities and conditions to test that with no environmental conditions in play, so this just chalk it up to wind and etc.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">There is a simple answer to spin drift, its called a ZERO. People sure seem to complacate shooting.

Seeing the lack of cleaned 1000 yard targets (with about a 2 min 10-X ring), I think spindrift is the last thing we need to worry about.
</div></div>

Maybe because they are not paying attention and calculating for that spin drift is why targets arent being "cleaned". Hell I know people that shoot KD comps who cant their optics to offset the spin drift in thier bullets. I guess they wasting their time too.

Thanks
 
Re: Spindrift Calculation??

Look on the right side of the program screen, where there is a box labeled "Calculate". One of the buttons is labeled "Deceleration K".

Use that to tailor the program output to your field shooting results.
 
Re: Spindrift Calculation??

All those programs mentioned, included the ABC, do not really "calculate" spin drift. Some have a built-in library for simplified calculations with specific bullets, and/or give a guesstimation of spin drift based on TOF, all based on real world data for a few bullets.

But different bullets will have different spin drift values, and this varies with barrel twist too. The only way to know how a bullet/barrel combo behaves regarding this hard to identify second degree effect is to have doppler data.
 
Re: Spindrift Calculation??

Tiro,

Well the ABC program is written from doppler radar data so I would say they are calculating it and not guesstimation of it. Yuma will tell you that Cheytac has more rounds on radar than anyone else out there.

Thanks
 
Re: Spindrift Calculation??

The only way to have accurate spin drift data is to shoot in a tunnel, so that there is no crosswind influence. No one I know is doing that at very great distances.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">The only way to have accurate spin drift data is to shoot in a tunnel, so that there is no crosswind influence. No one I know is doing that at very great distances.
</div></div>

Maybe one of us wizards can borrow the Hadron Collider for a day and test that out?

smile.gif
 
Re: Spindrift Calculation??

Later, the ABC program does have real world data imput in its built-in library, FOR CERTAIN BULLETS used by the military. As you probably know, most commercial bullets are not tested this way and certain properties necessary for the calculations are not available to anyone.

All the other program's accuracy (...and the ABC if it can be used for bullets not tested with radar data) are just a guesstimation.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChadTRG42</div><div class="ubbcode-body">I actually downloaded the trial version of Precision Shooter's Workbench yesterday. It takes a little bit to set up. The results do not follow my field elevations like some other programs do. It takes me 23.5 MOA to 1000, and it says 25.2 MOA. But, it could be me just not having all the proper fields filled in, or the program using different drag functions and such. I am not familiar enough with it to know the ins and outs yet.

http://www.precisionworkbench.com/ </div></div>

Chad,
Like Lindy said, there is a function on the right side that allows you to solve for "Dk". You need to actually do some firing in order to have an input for the calculator though. Once you solve Dk, the program will be spot on.



Cheytac ABC:

The spin drift figures I posted above come from a special screen that shows the shooter what was factored into the firing solution(spin drift, coriolis,movers, etc.). It is all integrated into the solution though so it's pretty dumb dumb. I recently took almost two years of firing data (elevation only) from my .260 data book, and compared it with the Cheytac solutions. The deviations at every yardage were inside .2 MIL (from spot on, to a max of .2 mil off)at ranges from 400 you 1100 yards. I didn the same test with FFS and got nearly identical results with some careful Dk tweaking. I was initially concerned that different rifles of the same caliber would make for different dope due the individual nature of the barrels. As far as I can tell, it just isn't a problem because the solutions are just spot on at the range window I am shooting in. I'm not saying different velocities make for the same dope, but inputing correct velocity and weather data makes for a spot on solution.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">Later, the ABC program does have real world data imput in its built-in library, FOR CERTAIN BULLETS used by the military. As you probably know, most commercial bullets are not tested this way and certain properties necessary for the calculations are not available to anyone.

All the other program's accuracy (...and the ABC if it can be used for bullets not tested with radar data) are just a guesstimation. </div></div>

I have the entire Cheytac bullet list and it is vast! It includes a bunch of hunting bullets as well. Only a fraction (maybe half) of the bullets on the list I would consider "military", and thats being generous.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">...inputing correct velocity and weather data makes for a spot on solution. </div></div>

The inverse of garbage in, garbage out, is still true.

And muzzle velocity changes with temperature - it's important to know what that change is to get any ballistic program to make good predictions.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Later</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jwp475</div><div class="ubbcode-body"> All bullets do not exhibit spin drift and I dought the 190 SMK will exhibit any spin drift. Very long extremely high VLD or ULD bullet can exhibit spin drift.
</div></div>

Are you for real? I suppose that radar range at Yuma is just useless and provides wrong data generated even though they have cameras and sensors every 25yards. Maybe someone should tell the bullet manufactures, ballistic program writers, etc that they are wasting that 25K per day to shoot thousands and thousands of bullets at the range to gather true downfield data.

The deal with spin drift is very few people have the capabilities and conditions to test that with no environmental conditions in play, so this just chalk it up to wind and etc.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">There is a simple answer to spin drift, its called a ZERO. People sure seem to complacate shooting.

Seeing the lack of cleaned 1000 yard targets (with about a 2 min 10-X ring), I think spindrift is the last thing we need to worry about.
</div></div>

Maybe because they are not paying attention and calculating for that spin drift is why targets arent being "cleaned". Hell I know people that shoot KD comps who cant their optics to offset the spin drift in thier bullets. I guess they wasting their time too.

Thanks
</div></div>

Yea I'm for real, I got my info from Mr. Perry of Perry Systems the creator of Exball. Why don't you call him and tell him that he doesn't know what he's talking about.

http://www.perry-systems.com/
email him and ask him yourself
 
Re: Spindrift Calculation??

The reason what got me going on all this was I missed a 10" plate at 1000 our last match, where I nailed the 600, 700, and 800 yard plates first shot. For once, there was no wind, and the mirage was straight up the whole string. It was a perfect condition. When I missed the plate, I could measure it to 1/2 MOA right with my reticle. One my second shot, the mirage was bending to the right, and threw me off to the right a little more. So, all this got me thinking. I like to make first rounds hit, since they are worth more in tactical shooting.
I think knowing everything about what might cause a shot to go wide at that range (or further) in perfect conditions will seperate you from the next guy in a match. In F class, I don't think it's as big a deal, since you have spotters to get you on target. I, too, know shooters who shoot a canted scope just for this reason. So, I want to get all the info I can, and decide if I want to apply this or not. It looks like I will need to from the data I have seen. I'll experiment with it, and see if I truely meed to worry about it.
Thanks for all the input guys!!

Chad
 
Re: Spindrift Calculation??

Supersubes,

You need 6DOF calculations, and I highly doubt all the bullets in the library have radar data since it is very expensive and labor intensive to test them that way.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The Mechanic</div><div class="ubbcode-body">are you sure you were not canting, Chad? </div></div>

I could have been, but I don't think so. I don't have a bubble level on my rifle, but I lined up my reticle with the top of the targets, which are level. But that is a possibility.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jwp475</div><div class="ubbcode-body">
Yea I'm for real, I got my info from Mr. Perry of Perry Systems the creator of Exball. Why don't you call him and tell him that he doesn't know what he's talking about.

http://www.perry-systems.com/
email him and ask him yourself </div></div>

Well I dont have the need nor desire to call or email anyone. I know from time behind my rifles that IF I dont follow the spin drift as calculated by the Cheytac ABC then target is going to show the effects. So I guess we just gonna disagree on this one lol, and I not talking about 600 or 1K yards by the way.

Thanks
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">Supersubes,

You need 6DOF calculations, and I highly doubt all the bullets in the library have radar data since it is very expensive and labor intensive to test them that way.
</div></div>
Am I supposed to shudder at the thought of 6DOF calculations? Somebody told you that once and now your spewing it here.

So they spend several days at Yuma, fire hundreds of different projectiles over the fancy radar, and when it comes time to put it into software they just say "eh, lets ditch those pesky spin drift calculations, we'll just take a SWAG at it, the user will never notice". Sorry no that just doesn't sound right.

The lions share of the projectiles were tested at Yuma. They added more at a later date using similar equipment at a different location.

 
Re: Spindrift Calculation??

"Am I supposed to shudder at the thought of 6DOF calculations? Somebody told you that once and now your spewing it here."

Come'on, I know you cannot impress so easily somebody with a nick like "Supersubes"...
smile.gif


Seriously, are you certain about all this? Were ALL the bullets in the ABC library tested with radar data?

Perhpas we could ask Triggerfifty, he was involved with the early testing of the CheyTac and the ABC.
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Later</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jwp475</div><div class="ubbcode-body">
Yea I'm for real, I got my info from Mr. Perry of Perry Systems the creator of Exball. Why don't you call him and tell him that he doesn't know what he's talking about.

http://www.perry-systems.com/
email him and ask him yourself </div></div>

Well I dont have the need nor desire to call or email anyone. I know from time behind my rifles that IF I dont follow the spin drift as calculated by the Cheytac ABC then target is going to show the effects. So I guess we just gonna disagree on this one lol, and I not talking about 600 or 1K yards by the way.

Thanks </div></div>


Well, since you claim to know then why don't you just post the amount of spin drift that the 190 SMK has and help the original poster. I am sure that he will apprieciatet it.
 
Re: Spindrift Calculation??

Spindrift exists.

However, for most purposes, it's not very useful to attemp to compensate for it.

On a 1000 yard shot, it's less than the amount of wind drift caused by a 1 mph full-value crosswind.

I can't call the wind to an accuracy of one mile per hour.

Those who can should probably worry about the exact amount of the spin drift correction. I'll not be doing so.
 
Re: Spindrift Calculation??

My original intention for this question was 2 part. One, I wanted to know why I missed at 1000 in perfect conditions, and if spindrift was a factor. Second, my goal is to work up an accurate load with my 208 A-max, and try to push it to a mile- 1760 yards. So, at this distance, a lot of factors come into play. If I can figure out the spin drift for the 190, I should also be able to figure out the 208. So, that's my intention for all this. I did get some good feedback, and chatted with some of you by PM. Thank you for the good info!
 
Re: Spindrift Calculation??

I've just contacted CheyTac, and they confirmed that ALL their data in the ABC comes from radar testing of each individual bullet up to the maximum range. Nice to know not only for second degree effects like spin drift but especially for accurate drop/wind calculations downrange. We all know the published BCs in some bullets are not that accurate at long range.

That is truly impressive, AFIK it is the only commercially available program with this extensive data base.

The civilian model has only one wind section, but the current military version has several wind zones, a built-in compass and GPS, and provisions for real time imput via blue tooth of external range finder, wind meter, pressure, temperarature, himidity, etc. More complete for extreme long range shooting, but also faster to imput data and more automated to help in a stressful environment.

 
Re: Spindrift Calculation??

They also have about 250 more bullets to add to the ABCs in the near future to make it more user friendly for non military.
 
Re: Spindrift Calculation??

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
wink.gif
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....
 
Re: Spindrift Calculation??

Chad there was some weird conditions at Tac Pro that day>>> first thing i noticed was my dope was 1/2 MOA Low..plates 7,8 and 9 taught me that.

Second thing i noticed is at 1000 when i .shot, flags at midway 600ish were straight down to slightly left<<<<<<<<<<< (5 o'clock) flag at 1000 was slighlty 5 O'Clock right>>>>>>>>>>>>>...MIRAGE was running slow Left<<<<<<<<<<....Thinking to myself <span style="font-style: italic"> trust the mirage not the flags <span style="font-weight: bold">hold right edge</span></span> Shoot.... catch trace right at point of hold quickly being dumbfounded adjust, <span style="font-weight: bold">hold left edge</span>.. Shoot <span style="font-weight: bold">Ding</span>! still scratchin my head on that one.
 
Re: Spindrift Calculation??

My only contention with Tiro was that he was just assuming that Cheytac wouldn't possibly take the time to do the required calculations. Good on him for getting it from the horses mouth, something I had already done.

Cheytac takes the time to integrate spin drift into every calculation whether I want it or not. Guess I am stuck with it.

I completely agree with Lindy that we (I) cannot shoot "inside" spin drift error.

Mike D.
The "not enough range" time comment is BS. We are here to discuss precision shooting stuff. I would rather participate in this thread than the "whats the best scope for under $300 threads"
 
Re: Spindrift Calculation??

Yeah, I remember it switching some, and right before I shot, the mirage was straight up for me. The flags were running straight also. I remember it changing some to. I held no wind and straight on- missed just right. Then held left edge, and missed right again. Then I noticed the mirage running. Just one of those things!
 
Re: Spindrift Calculation??

Supersubes, I'm eating deep fried crow with extra cheese
wink.gif


Would you care to give us a few examples of spin drift value at one mile? Say with a .338" 250 gr Scenar, .338" 300 gr SMK, and some other load in 7 mm Rem Mag?
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">I've just contacted CheyTac, and they confirmed that ALL their data in the ABC comes from radar testing of each individual bullet up to the maximum range.
</div></div>

I'm unsighted on this software; but someone mentioned earlier that the program's bullet 'library' was huge. Clearly that can mean different things to different people; but if that means:

<span style="font-weight: bold">each maker </span>at
<span style="font-weight: bold">each bullet weight </span>at
<span style="font-weight: bold">each calibre </span>at
<span style="font-weight: bold">each spin rate</span>,

that's <span style="font-weight: bold"><span style="text-decoration: underline">a lot </span></span>of different bullets and barrels.

In that context, their claim would seem a little.... er.... '<span style="font-weight: bold"><span style="text-decoration: underline">unlikely</span></span>'
smile.gif


and...assuming the library is indeed 'large'; it doesn't survive a common-sense check.


I have trouble believing their calculations are anything more than as described by Tiro initially:

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">All those programs mentioned, included the ABC, do not really "calculate" spin drift. Some have a built-in library for simplified calculations with specific bullets, and/or give a guesstimation of spin drift based on TOF, all based on real world data for a few bullets.
</div></div>

<span style="font-weight: bold">Could someone clarify just how many bullets this fired radar data is claimed for

...ie how many bullets are in the 'library'?</span>
smile.gif
 
Re: Spindrift Calculation??

Brown Dog, they said: "we use a different mathematical paradigm or modality to do the calculations"... and that they have doppler radar data for 300+ bullets.

I'm pretty sure the calculations are simplified, but when we talk about second degree effects like spin drift perhaps they have a way to figure out at least in which "bracket" the tested bullet fits.

In any case, if it is based on radad data it is a huge step ahead than just a gesstimation based on known spin drift values of a few bullets.
 
Re: Spindrift Calculation??

Tiro,

Aha! All becomes clear!

Definition of <span style="font-weight: bold">paradigm</span>:

"example, pattern; especially : an outstandingly clear or typical example or archetype"




Thus, in saying <span style="font-weight: bold">"we use a different mathematical paradigm or modality to do the calculations"... </span>

they're actually saying that <span style="font-weight: bold">they're not calculating it in the ballistic computation sense</span>;

<span style="font-weight: bold">nor looking it up in a library of fired data for every bullet</span>;

but simply (despite the complex language!) <span style="font-weight: bold">approximating</span> it from <span style="font-weight: bold">similarities</span> to a '<span style="font-weight: bold">similar</span>' bullet.


I still think you were spot on first time!!
smile.gif
 
Re: Spindrift Calculation??

While were discussing balistics it takes a liftime to understand, what is the name of the effect concerning time of flight and the rotational spin of the earth past 1200 meters.

Buck
 
Re: Spindrift Calculation??

Subes-
Acually your snippy retort is a classic symptom of too much computer time vs range time. To compare spin drift to best cheap scope debates????

Settin a low bar aintcha???

I feel that too many times too many 'educated' types think wavin the technology wand around makes it true true true. fact is mumbo jumbo like mathmatical pair of dimes is a 5 dollah phrase for a 3 dollah word... extrapolate.

But back to the real world. A few shooters have said that in thew grand scheme of things spin drift doesnt mean much to a tacticool shooter. First round misses cant be blamed on spin drift, nor does spendin hours online or runnin numbers bring ya closer to a first round 1000 yard hit.

Spendin time dancin with the wind n learnin what terrain does to windflow beats computer dis-cuss-ions. Course those who cant get to a long range venue are free to pick nits off the butt of the nit on the butt of the nit that is on a wind shift's butt.

I guess if ya cant speak on what really pooches long range marksmanship ya will discuss spin drift, cor-a-silly-us effect n of course tidal pull on months endin in R....

Continue on, I was just tryin to bring some reality to a rather myth filled discussion...
 
Re: Spindrift Calculation??

Brown Dog, you have a way with words
wink.gif


I'm trying to find out with the CheyTac people if their radar data is just TOF and trajectory, or if it also includes bullet yaw. The TOF/trajectory testing would at least give a very accurate description of the bullet decceleration rate, and it will be very useful for drop/wind corrections.

If they make the second degree effects calculationes like spin drift based only on TOF then it is going to be pretty inaccurate unless the specific bullet/load/barrel combo is very similar to the "paradigm". This is the case with most other programs.

But if they have records of bullet yaw they can make a much more accurate estimation based on other well tested bullets. Sure there would be variations, but the effect would be minor if you are close to the tested conditions: specific brand, model and caliber of bullet, muzzle velocity and barrel twist.

IMO it would be nice if they make all this clear in their literature. The radar testing and program features seem like a step above the competition.


Edited to add: even though wind estimations reigns supreme, I think an accurate estimation of spin drift is quite important at very long ranges.

In a military table I have the .338" LM 250 gr Scenar has about 0.8 mil (2.75 MOA) of spin drift at 1500 m. Pretty significant if you ask me...
 
Re: Spindrift Calculation??



Mike D & Lindy summed it up pretty well IMHO
 
Re: Spindrift Calculation??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mike D.</div><div class="ubbcode-body"> Cantin a scope-
I've seen a few do that, I heard it was because David Tubb did it once
wink.gif
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...</div></div>

If everyone recalls we went this road once before. After DTUBB posted, I made a change in both the .308 win and the 300wm. With the weapon level via USO's bubble's being set via a known level on the base, I 100 yrd zero'd dialed 35moa for the .308 (175smk)and kept changing the cant to the left until the weapon was poa poi at 100yds and 1moa to the left at 35moa up, on the same target. (The 300wm (190smk) being 5/8moa to the left.) Now at 1k I need no left wind added when the wind is very slight from the right. DTUBB said from a 300yd zero with a match .308 there was just about 1moa of right spin drift, and moving from 300 to 100 it was 1/4moa left IIRC. All this assumeing the tube has right hand twist rifling.
I know nothing about anything but, I do know I dial less left wind now than before, when both sticks printed straight up the target at 100yds when dialed for 1K. YMMV

The short cut to getting it close right out of the gate is run a plum line starting at your poi up to your 1k up setting. Then mark the target the correct moa to the left. Now while the weapon is locked down cant the scope until the upper cross hair is lined up with the left hand mark and the X hairs are still on the poi zero. Saves ammo this way and sometimes you get lucky the first try. Again YMMV
 
Re: Spindrift Calculation??

Mike seriously, I wasn't attacking you. Can i EXTRAPOLATE that since you have posted 7751 times you have missed wayyyy more range time than I have? You make improper assumptions about my or anyone elses range time based upon what we are talking about in an internet forum! The reality of spin drift has was posted and acknowledged before you added your two cents.
 
Re: Spindrift Calculation??

Tiro,

drift figures at 1760 yards:
.338 300gr SMK @2750 fps 1.97 MOA
.338 250gr Lapua @2950fps 2.58 MOA
7mm J40 162 gr @ 3050fps 1.23 MOA
7mm 160 gr sierra gameking @ 3000 fps 2.94 MOA

I don't own a 7mm so the bullet library in my device doesn't include many of them. The full library is not loaded into the device because it slows down the software. Bullets are easily downloaded from one of their websites so you can make your own custom list.
 
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