Range Report Spin Drift

[muleman]

When I get to 900 yds it seems I consistantly shoot a little right 3-6". When I get to 1000 I consistantly shoot 6-10" right. I don't notice much off at 800yds and under. If I correct windage for this I'm then off a little LEFT at 800 & under, What could be causeing this, Spin Drift? Shooting 300WM 208 Amax 2940fps. I haven't gone past 1000 to see if it gets worse.

 

[USFTR]

Re: Spin Drift

Sounds reasonable to me. I see the same thing if I zero at 200 yds and then back up to 1000 (assuming the wind is dead).

 

[MitchAlsup]

Re: Spin Drift

If I remember correctly, spin drift of a 308 at 1000 yards should be on the order of 2-3 inches (maybe 4 inches) and basically invisible (down in the noise) closer than 800 yards. This might account for 1/2 of what you are seeing.

 

[Graham]

Re: Spin Drift

I doubt that it's spin drift. Trigger control could cause a left-right shift like the one you described. It could also cause the 3-6 and 6-10 that you talk about. I can neither hold nor determine .3 MOA on a target at 900 yards: are you shooting benchrest? What caliber?

 

[Alpine 338]

Re: Spin Drift

I noticed the same for the first time last week, shooting 308 175-gr SMK at close to 1000-yards. I corrected for it, then back home I noticed that now at my 100-yard zero I'm shooting 1-moa left and 1-moa down. I never noticed this before because once I sighted in at 100-yards, I just corrected for shooting beyond 300-yards.

 

[AQC440]

Re: Spin Drift

Cross hairs in the scope canted slightly in the counter- clockwise direction?
If that were to be the case, when you sight through the scope and by instinct hold the cross hairs perpendicular POI would shift to the right with a bit of vertical as well.

 

[UKDslayer]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Alpine 338</div><div class="ubbcode-body">I noticed the same for the first time last week, shooting 308 175-gr SMK at close to 1000-yards. I corrected for it, then back home I noticed that now at my 100-yard zero I'm shooting 1-moa left and 1-moa down. I never noticed this before because once I sighted in at 100-yards, I just corrected for shooting beyond 300-yards. </div></div>

If you went to another range, did some distance shooting, came back and your "cold bore shot" (in essence) changed, my questions would be 1) is your scope lock-tight (literally "Loctite") solid or could it have moved in transport - this is much more common that you think, 2) any conditions such as temp., barometric pressure significantly changed at your home (100yd) range,was it noted in your logbook? 3) if you use a can was your can on tight (also moves in transport), and 4) any other issue pertaining to the "cold bore shooting" come in to play?

 

[UKDslayer]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: muleman</div><div class="ubbcode-body">When I get to 900 yds it seems I consistantly shoot a little right 3-6". When I get to 1000 I consistantly shoot 6-10" right. I don't notice much off at 800yds and under. If I correct windage for this I'm then off a little LEFT at 800 & under, What could be causeing this, Spin Drift? Shooting 300WM 208 Amax 2940fps. I haven't gone past 1000 to see if it gets worse. </div></div>

A velocity of 2940 should be enough that true "spin drift" isn't in play. I'm betting its good old wind, or even those "vortexes" we've all encountered that changes direction of wind between one target and the next 100 yards later. "Believe the bullet".

 

[ewoaf]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: UKDslayer</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: muleman</div><div class="ubbcode-body">When I get to 900 yds it seems I consistantly shoot a little right 3-6". When I get to 1000 I consistantly shoot 6-10" right. I don't notice much off at 800yds and under. If I correct windage for this I'm then off a little LEFT at 800 & under, What could be causeing this, Spin Drift? Shooting 300WM 208 Amax 2940fps. I haven't gone past 1000 to see if it gets worse. </div></div>

A velocity of 2940 should be enough that true "spin drift" isn't in play. I'm betting its good old wind, or even those "vortexes" we've all encountered that changes direction of wind between one target and the next 100 yards later. "Believe the bullet". </div></div>

I'm with UKD, I dont ever really see any spin drift at all myself shooting at 1000yd w/ my .308. I'd also lean towards trigger pull or canted scope.

 

[goober]

Re: Spin Drift

Muleman , believe the science and ajust for it because it is there even if your not a good enough shot to make it work for you there is no excuse not to allow for it -give yourself the best opportunity and stack the math in your favour

 

[stenger]

Re: Spin Drift

i have the same problem shooting many guns and even my benchrest guns do the same thing. it is there and you have to account for it. i only shoot off a solid benchrest rest and still have the same problem even with the gun level and the rest level. the scope has also been leveled to the action on all on my guns. i know at 1200 yards i was holding 3/4min for hits and at 600 i hold about 1/4 min. i have tested this theory in 0 wind conditions with wind flags. it's there for sure.

 

[Lowlight]

Re: Spin Drift

Unfortunately it doesn't quite work that way...

While it is a scientifically backed occurrence, external factors, including the human factor by far outweigh it. And I'll explain...

First off, let's take the rifle, if you have a rifle capable of shooting 1 MOA at 1000 yards, a portion of that group will be left of center, so the portion that lands left, will negate the effects of SD. The ones that go right of center will have the SD error compounded. Only the rounds directly above or below center will fall within the adjusted range. Now put a 1 MOA shooter on that same rifle and the results become even more dramatic. So this is the first and foremost reason why it is considered <span style="font-style: italic">"noise",</span> because of the inherent accuracy of the system to include the shooter... SD doesn't mean all the shots that are fired are going to land a prescribed amount to the right of center,only the ones in line with center will go that far to the right, the other may land right but that happens to be center on the target because they started out left. Another thing in this system, scope manufacturers will allow for a 2% error from one optic to another, and in some cases that 2% can be as much as 5%. This is a cross section sampling that says, you scope can have issue, yet still be acceptable for sale. How many have actually checked their scopes adjustment all the way to distance measuring the value of the adjustments and whether or not they track solid to 40 MOA ? Most don't, and a lot of scope errors only become visible at distance. Especially if you are running it to the edges of its adjustment range. The internals can move the erector any little bit off without you ever knowing it.

Next and this is something I have personally witnessed and took note of... Right handed shooters versus left handed shooters in field conditions.

Let's get off the fixture and move to the field with an actual person shooting. I have witnessed as much as 2 Mils difference between a series of shooters on numerous occasions when engaging the same target. This means more than 70 inches of difference downrange between a series of shooters using the same rifles and ammo on the same target at the same place. Where, on the far end the furthest right handed shooter will need more than 3.5 mils to hit a 1000 yard target, on the other end a left handed shooter needed only 1.5 mils to hit the same target on the same line. I have made a point to record this in class after class and it almost always lands around 2 mils between the two. A right handed shooter will tend to pull the rifle right, the left handed shooter will pull the rifle left completely blowing the science away from the reality on the ground. In a fixture under scientifically controlled conditions we have one value for SD, in field conditions with a different set of shooters we have another, and neither set of results will match. The majority of shooters are right handed, which is why many will see drift to the right as opposed to the left. But left happens. If you watch the video we did, using the pad of the finger versus the joint, you'll note at 100 yards we saw next to know difference shooting the same rifle and ammo. However at 300 yards it was the difference between a series of groups that averaged .5MOA versus a set that measured 1 MOA. Alternating your trigger by simply moving the finger from the pad to the joint completely changed the accuracy dynamic of the system. Imagine from a right handed shooter to a left, or one person with a good trigger versus one with a poor trigger.

To that fixture...

Let's look at the twist of a rifle barrel. Did they use a 1-12, 1-10, 1-11.25, and how was that barrel made, because the twist will have a significant factor in all of this. If Barrel maker "A" uses a new tool and cuts 100 barrels with it, as each new barrel is made, a different twist will result. So the exact value of the twist in barrel number 1 will not match the same twist value in barrel number 100. So which barrel exactly do you have... one closer to the new tool, or one closer to the tool near the end of its life ? This matters, yet goes unanswered, they all say 1-X, but it is 1-10.1, 10.2, 10.5, 10.7, or 10.9 ? That is an effect science can account for yet doesn't have the vehicle necessary to do so.

Next we had the <span style="font-style: italic">"no wind day"</span> well I personally have never witnessed a <span style="font-style: italic">"no wind"</span> day, and find it strange that people mention it because they always mention coriolis along with SD. When you get up in the morning before you shoot, look at what the weather channel says for your prevailing wind conditions in you area, and record any <span style="font-style: italic">"no wind"</span> days. Because if the Earth is rotating, it is moving air... and that movement is what effects the bullet. Just because you don't feel the wind proper, doesn't mean it isn't there. For coriolis to be a factor you have to have wind, because you can't acknowledge the earth is moving but the air is not. Look at Humidity, people think that because they feel the air as heavy so does the bullet, yet we all know humid air is "less dense" than drier air. But so many get that wrong, including the manuals put out by the military. 1 MPH of wind is more or less in line with the standard understanding of SD to be using a .30 cal bullet. So unless you can say that over a 1000 yards distance you can figure for 1 MPH of wind, you are losing it in the noise of the environment around you. Remember the higher you get off the ground, the more wind will be present. If you read a 5 mph wind at the ground, you may have as much as an 8 mph wind at Max Ord of a 308 reaching out to a 1000 yards. So if you have 1 MPH on the ground, you might have 3MPH up there, more than doubling your wind drift. I know very few people who can even attempt to call wind to within 1 MPH.

With the advent of computers, modeling competitions, ballistic calculators, we find more and more people are blaming spindrift for errors in their shooting, which as always are mainly trigger control and follow through problems. Where here, me as a graduate of Marine Sniper school, never once accounted for it yet qualified at distance without it. In fact the USMC manual makes no mention of it. So the question begs, how did we do it ? Interesting to note a "Tactical Version of Field Firing Solutions was written with USMC input and they asked that SD be removed from the version. My guess, because it is noise and confuses the issue. So one has to wonder, how so many people have managed to over look this factor, yet hit targets ? Luck or the understanding with the proper execution of the fundamentals comes success, and not a static 1 MOA left adjustment. Funny thing is, with most ballistic computers, if you change the zero range on the model, say from 100 to 600 yards, the spindrift value for that 1000 yard shot remains the same. However if you zeroed your rifle at 600 yards you have effectively zeroed out the effect of SD, it would realistically start over or at least be significantly less down range. However since they don't know what your rifle is like they basically just give you a flat rate value to use, figuring it is close enough for government work.

Yes SD exists, however can a shooter under field conditions utilities the adjustments needed to counter it -- well that is to be debated because of these factors. Rifle, Barrel, Scope, Shooter. In field conditions most fail to hold 1 MOA, in fact many who can hold .5 MOA at 100 cannot hold 1 MOA at 500, let alone 1000 yards, so exactly how are you supposed to implement this kind of deviation when you can't tell it apart from your own errors or the errors built into the system. Most are simply dialing their poor trigger control I am sad to say, and simply don't know any better. Only on the internet do people actually account for actual SD, rather than these factors.

 

[USFTR]

Re: Spin Drift

I didn't realize this was such a touchy subject! I do believe spin drift exists because of what I have seen over a few years of shooting. In my opinion, it is relatively small, but present and meaningful on the small F-Class targets and I do adjust for it. Can wind be causing what Wayne is seeing? Sure, but given enough times to the range, the trend will be obvious. The mirage can be running right to left just barely and still my round will impact a few inches right at 1000 yds. I can't really detect a difference at 600 vs my 200 yd zero.

 

[Graham]

Re: Spin Drift

You're out-clevering yourself. Go back to the basics, and to shorter distances. Start at 300.

 

[Graham]

Re: Spin Drift

I mean that you are looking for a fancy explanation for a very simple problem.

Maybe it's that the world begins at 900.

 

[sinister]

Re: Spin Drift

Chapter 9.

 

[USFTR]

Re: Spin Drift

For my standard load in .308 Win, I calculate a 6" drift at 1000 (about 2 clicks is what I have noticed). Plug in your numbers in JBM (barrel twist, BC of bullet, velocity, length of bullet, etc) and you will see about how much to expect. Plug in 0 wind.

 

[Swan]

Re: Spin Drift

With my current load inputed in JBM I get about 0.1mil of drift at 500yds and apparently 0.2mil of drift at 1000yds. This is very unsettling news, as I hate it when "outside forces" influence my shooting (wind, coriolis, spin drift, hangovers, etc.). So I have decided to just start shooting left handed and purposely jerk the trigger a bit... to compensate.

 

[Lowlight]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Swan</div><div class="ubbcode-body">With my current load inputed in JBM I get about 0.1mil of drift at 500yds and apparently 0.2mil of drift at 1000yds. This is very unsettling news, as I hate it when "outside forces" influence my shooting (wind, coriolis, spin drift, hangovers, etc.). So I have decided to just start shooting left handed and purposely jerk the trigger a bit... to compensate. </div></div>

Just zero you rifle 1/3 of an inch to the left of center. Problem solved, except when you Influence the trigger enough to have to dial left for a right to left wind as someone here stated. Especially when you consider a 1 mph wind will move the bullet 10", you have some real SD going on when you out spindrift the wind drift.

 

[Swan]

Re: Spin Drift

I think I'm gonna paint that on my rifles now:

<span style="font-style: italic"><span style="font-weight: bold">"I out spindrift the wind drift"</span></span>

 

[Guest]

Re: Spin Drift

Spin Drift whats that?

 

[ewoaf]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gunfighter14e2</div><div class="ubbcode-body">Spin Drift whats that? </div></div> It's what you use as an excuse when you're oh so sure it just can't be you.

 

[Guest]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ewoaf</div><div class="ubbcode-body">It's what you use as an excuse when you're oh so sure it just can't be you. </div></div>

That may be true, but I liked DTubbs an NASA's rendering better. We have kicked this Dog, many times over the years.

 

[Lowlight]

Re: Spin Drift

I like the emprical data that can be found in places like the "Practical Tactical Thread"... I think it demostrates the point better than any written description.

Stuff like this:

it shows a very good zero, and tight centering, however as you continue

A pattern starts to appear

Now take the data that is illustrated here and look at the statics it renders for the viewer. And there are six pages of this kind of stuff.

You can see a consistency that begins to form, low right, low right, or even just right of center:

Pages and pages of this, shot at 100 yards were we know the outside effects have very little affect on the shots.

Post after post by many different people, not just the same person over and over, right of center, right of center, right of center. What do we think stuff like this does 1000 yards downrange ?

I think it speaks volumes... but still, science, computer modeling and ballistic programs can't be wrong.

They explain it so much better than rounds downrange every could.

Great thing about the internet, you can find an answer to almost anything.

 

[Guest]

Re: Spin Drift

I agree I see a pattern. Are these from the school or from Hide shooters sending them in?

 

[Lowlight]

Re: Spin Drift

These are right off the site, when we shoot these targets during classes, the patterns become even more apparent, I need to start keeping them.

This reflects the reality of people's shooting, on a much boarder scale than most would like to admit. Not that there is anything wrong with it, however we are much more responsible for misses than things like SD.

If the OP was saying he was seeing this problem at 1500m I would be all about the necessity to adjust for SD, however at 1000 yards with a 300WM, that is more than likely trigger... I believe the doppler numbers for the A191 only record 5" of SD at 1000 yards, so anything "more" is most likely shooter induced. SD is what it is when all else is perfect, when one leg of the fundamentals table is compromised all bets are off, compromise any more than single leg, well you get the point.

 

[AQC440]

Re: Spin Drift

OP! Glad you found <span style="text-decoration: underline">your</span> answer.
I after many hours of dry firing, watching the cross hairs for absolutely no movement on distant targets during the trigger break, using just the pad of my trigger finger with the least amount of small muscle groups involved as possible, have somehow seemingly defeated SD with-in 1000 yds…

 

[Guest]

Re: Spin Drift

I'll agree we, are the biggest factor when it comes to shooting over moa at any distance when mother is being your friend.
That said, I still prefer a canted reticle, if just to cut the excess numbers being ran at the time. Can I read the wind closer than SD really is at 1000yds for a .308win throwing 175smk's no I can not. However If I can make a gear change that greatly reduces or nulls an issue to save time, I'm all about that.

Chasing last hits has never taught me anything but how follow up quicker, or knob, or reticle faster. This is why I always start far if I can, just to see if I'm learning anything or still just burning powder.

 

[Graham]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: muleman</div><div class="ubbcode-body">I've found my answer, for those that care to know....They didn't state velosity or rate of twist but this explains what I seeing.</div></div>No it doesn't. If it did you would see a bigger problem with 8-twist and 80 grain bullets than with a 9-twist and 68grain bullets.

 

[Lowlight]

Re: Spin Drift

Canted Reticles are a whole other ball of wax.

1. The mind wants to naturally straighten things,

2. Your dependent on a bubble level

3. You can't see your level at night

4. Support side shooting, enough said.

We've seen the canted reticle thing tried and fail in spectacular fashion. It's fine if you shooting high power at Raton, but under field condition, under stress,it falls to pieces for everyone but David T.

 

[sobrbiker883]

Re: Spin Drift

Interesting stuff. I usually click on .2mil left past 600 yards then hold for wind.
I just had my 7/08 apart and I think when I confirm my zero I'll shoot for the 1/3" left on my 100 zero and see how that shakes out. Most of my groups have the same pattern that are apparent in LL's reference to the Pratical targets

This reminds me of the 1/4 vs 1/8 moa windage sight debate Service Rifle shooters always are engaging in.......

 

[Swan]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sobrbiker883</div><div class="ubbcode-body">Interesting stuff. I usually click on .2mil left past 600 yards then hold for wind.
I just had my 7/08 apart and I think when I confirm my zero I'll shoot for the 1/3" left on my 100 zero and see how that shakes out. Most of my groups have the same pattern that are apparent in LL's reference to the Pratical targets

This reminds me of the 1/4 vs 1/8 moa windage sight debate Service Rifle shooters always are engaging in....... </div></div>

Not sure if LL was serious about the 1/3" left statement but it did remind me of a discussion I had with some fellow shooters about a month ago. 0.1mil turrets and not being able to get a fine enough zero for matches (always a lil left/right of dead nuts). Our conclusion was to zero a bit left anticipating the trigger jerk in stressful, fast stages. Seems to work most of the time... I think.

Seems like a remedy for spin drift as well.

 

[error4o4]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinister</div><div class="ubbcode-body">Chapter 9.

</div></div>

Came here to post this. I'm just finishing it up, and it's a great read. I would recommend it very highly to anyone wanting to learn the fundamental aspects of ballistics.

 

[idahohunter]

Re: Spin Drift

Dude ur right on the money...at 1,000 i need .75 minutes left for spin drift with a 300 gr smk at 2800 fps. Now understand when the wind is blowing this is too subtle to see. Really the only way to see spin drift is ABSOLUTLY no wind and you have to be holding rock solid, even a little twitch in your trigger pull will cancel out the ability to see spin drift. Most guys i know don't even allow for it, cause they are so used to figuring the numbers with wind (if that makes sense)

I only shoot aobut twice a year or so at 700 for validating trajectories only, the other 90% of my shooting is 1,000 and beyond. But even at 700 on very very calm days, I need to correct 1/2 minute left for spin drift.

chow

 

[Graham]

Re: Spin Drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: idahohunter</div><div class="ubbcode-body">Dude ur right on the money...at 1,000 i need .75 minutes left for spin drift with a 300 gr smk at 2800 fps. Now understand when the wind is blowing this is too subtle to see.</div></div>3/4 MOA at 1000 equates to how many mph of wind? Is that enough wind to miss your target? If so, is that too subtle to see? OK. So, half-minute is 3.6" at 700 yards; how big are your groups at 700 yards?

 

[Lowlight]

Re: Spin Drift

Telephone... just like I used to see on Wonderama.

Now the 338LM has the same SD as the 308 ... the legend continues to rise with each yank of the trigger.

Maybe we need to invent a clever way to explain the phenomenon called , "dialing a flinch", so it doesn't sound so negative. Something like, <span style="font-weight: bold">Distal Offset Adjustment </span>

<span style="font-style: italic">what I want to see is a video of each person shooting who is advocating these numbers.. focus on the firing hand please for at least 3 shots. </span>

 

[Wil]

Re: Spin Drift

What we need here is some good 'ol Tokyo Spin Drift.

 

[Shady_Jay]

Re: Spin Drift

ripping off my old jokes, huh?

 

[Graham]

Re: Spin Drift

Uh Oh... The Texas boys have arrived on the Thread.

Sealt belt: ON.

 

[hexades1]

Re: Spin Drift

Bryan Litz (Berger Bullets ballistician) has created a formula for calculating spin drift that takes into account the bullet length, twist length and bullet speed. It has been used quite a lot here in Finland since his book came out. Before that we used a formula from a book sold by Border barrels. Of course lots of shooting in all conditions has been used to validate things too in the last 10 years or so.

For my 338LM with 907 m/s 250 Scenars reload I put 0.1 mrad correction between 650 and 950 meters. Add one 0.1 mrad more at 1000m and a 3rd 0.1 mrad at 1200m.

So my formula is

0-600, no correction
650-950m, 0.1 mrad to left (RH barrel)
1000-1150m 0.2 mrad to left
1200m 0.3 mrad

For longer ranges one could calculate the drift but wind becomes so difficult to read that some of the added corrections fade into the noise os I do not really bother as I get to shoot over 1200m maybe two times a year.

Three weeks ago I made a 1st round hit at 1400m in windless morning conditions to a upper body reactive target with the SAME elevation and SPin Drift correction I used in 2007 at the same range in summer (same rifle, same optics, same type of reload and same env. conditions) prove to me that I either correct for the Spin Drift with my rifle/optics/ammo combo or I do not connect with the target. BTW the 1st round hits were cold bore shots with barrels cleaned the night before both in 2007 and 2010. I would say the system shoots whenever I can shoot up to my best ability (which is not so often

So yes spin drift does exists and at 1000m or more you need to correct for it to enhance your chances to hit your targets. Of course you can be lucky and hit anyway without any corrections but I prefer easy field solutions.

Below 600m do not worry about it.

 

[hexades1]

Re: Spin Drift

Ask Bryan Litz about it if you do not believe me. He can explain it better because he IS a bonafide rocket scientist

 

[Lowlight]

Re: Spin Drift

Interesting I can make many first rounds hits too without it... so one has to ask what am I doing differently and I have a history of shooting places like ASC with many others which is all about 1 shot. I actually tied DTUBBs score at the Raton Sporting Rifle match and didn't use it, 1 shot per target only for 60 shots and I scored a 56.

And by your number, 950m, 1038 yards, you are using .36 of an inch, where as the poster above is using double that distance. .75" so this sliding scale, of Drift is what becomes the issue.

Not to mention you fail to include the discussion of the width of a reticle at 1000m, what does it cover on a P4, 60cm ? How much is your drift again ? Or how often to you consistently hold the reticle to one side more than the other ?

yes it exists, however if you look at what Rick Boucher from the Army Sniper School said years ago, and was what I was taught as well... it is far below the numbers posted today. Like a game of telephone, look at the date of this post:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Guys, I mentioned spin drift for the fun of it. A normally weighted and stabilized bullet travels nose down during descent of trajectory and normal spin drift occurs in the direction of the spin, ie right for right spun barrels. This drift would run about .25 moa at 1000. We use spin drift for the 168 because of the rounds tendency to fall nose high from being over stabilzed past 700. This drift runs about .5 moa at 800. This is farther than you should shoot that bullet. It is optimized for 600 yards or about 554 meters.

Rick <RBowcher@XXXxXXX
Fayetteville, NC USA - Tuesday, October 13, 1998 at 21:39:17 (EDT) </div></div>

I have heard people put it as high as 2 MOA at 1000 yards, and that is 2MOA at the shooter, so we have a scale that slides from .25 to 2.

Litz qualifies his answers on the subject, but almost completely discounts the shooters, and simply talks about the wind, and not the shooter, the rifle or the scope ? He mentions wind..., and qualifies that not much else.

These numbers for SD exist <span style="font-style: italic">under perfect conditions</span>, however how many perfect conditions exists that incorporate, No Wind, perfect shooter, known barrel, etc. If your rifles works with adding .1MRAD at 1000m, great, that doesn't mean mine will or that your shooting and my shooting are the same... what is observed in a fixture is not the same as what is observed under field conditions by an actual person pulling the trigger.

I challenge you on the next <span style="font-style: italic">"no wind'</span> day to put a left handed shooter on the rifle and record your results . Also, maybe you missed it, I also believe and have proven on numerous occasions most cold bore shots are induced by the shooter and can be significantly reduced or eliminated by proper application. So saying your cold bore hit is essentially a distraction.

Empirical data in this wins out, science to be valid must work the same for everyone and not be selective in its application, so modeling a number or saying one thing is what it is and not user induced it must apply equally across the board. The untested variables make it a wild card.

 

[USFTR]

Re: Spin Drift

I am amazed at the attitude of several people on this forum. Obviously there are two camps here with very different opinions. The respect shown for our fellow marksmen and competitors has gone down hill in my opinion. I do not profess to know all there is to know about shooting, but I hold true to my observations and beliefs. Lowlight, to make sure I understand your argument, you claim that spin drift is so small that no marksman can detect it and that any deviation from center is due to the shooter pulling the trigger to the side assuming no wind, which you say doesn't exist. You must then also claim that either myself and the others that claim we have seen it are just bad trigger pullers (I'll assume you belive what we have reported to have observed). Am I correct in my assesment of your argument?

Oh, and what size target are you shooting at for the one shot hits at 1000 yds (+/-) and the size of the longer targets at ASC?

 

[Shady_Jay]

Re: Spin Drift

F4U Corsairs used to barrel roll counter-clockwise to counteract the drift when shooting in the Eastern Hemisphere. It wasn't necessary in the Western Hemisphere due to a larger deposit of iron ore near Greenland.

 

[Swan]

Re: Spin Drift

This just keeps getting better.

 

[Lowlight]

Re: Spin Drift

usftr,

You are sort of over-simplifying what I am saying, but I will expand so you understand.

I am saying the variables involved in the shot at that distance are much more in-depth than just stating a flat rate number as advocated by many will work. And generally doesn't work for all. I see hundreds of students a year and consistently shoot out to 1000 yards under a variety of circumstances. Factors include:

Differences in Barrel Twists and builds... which directly effect changes in drift.

Differences in muzzle velocity and ammunition used

Conditions as they exist across 1000 yards plus, as much as 15ft above the line of sight - a 1 MPH mistake in the wind mean an much as 10" at 1000 yards, a 1/2 MPH mistake is roughly 5", so in order to "see" the difference you are saying over the course of 1000 yards, and 15ft above the line of sight you can judge the wind to 1 MPH.

The Shooter... including errors in trigger, follow through, position, NPA, breathing... all that can influence and do influence the course of the bullet.

Errors in the scope adjustment, inherent thickness of the reticle which covers more than than the stated SD value. Recent example of scope errors

As a point of reference, I will bring your attention to a document which discusses the variables which can effect a ballistic calculation when using a computer program. Ballistic Program Inaccuracies

The fact we can see, and have recorded as much as 2 Mils of difference in holds at 1000 yards between a left handed shooter and a right handed shooter speaks volumes to this subject of shooter induced errors. And cannot be overlooked by any stretch of the imagination.

That fact all the SD values I know of have been shot from only a limited combination of barrels and ammunition from a fixture. And that results from fixtures rarely translate accurately to humans under field conditions.

The inference that "no marksmanship can see the results, I never made, however I will contend that 99% of marksman cannot discern the accuracy necessary to utilize adding .1MRAD at 1000 yards. or .36" or an inch. as stated, from 650m to 950m, you are saying its 3.6" -- well that is very noticeable at 650, and much less noticeable at 950. If you think about that, for all the years we had wind charts, and used wind corrections people would have routinely recorded significant problems with wind charts that give an equal value from right to left, the left wind would be too much the right wind not enough if you are adding 3.6" at 650m. Rarely is this heard of... it's not until the advent of ballistics computers do we now see greater and greater need to adjust for SD... because they model it to fit a pre-designated program. Again, check your ballistic calculator for a 1000 yards no wind shot with SD and then change the zero range... my bet the number remains constant. In case you missed it the first time, the USMC asked that the SD adjustments be removed from the ballistic calculator they had a hand in working on. This I can show you has I have both copies, one with and one without.

My point is, being an instructor, I see all types of shooters, and a whole lot of trigger issues. The targets above are repeated over 7 pages, and then more numerous types across a variety of shooting websites, not just this one. The pattern is clear, the errors point to pulled shots that go right generally a 1/2" at 100 yards, and that shooter above was consistently hitting a 1/4" dot, except when pulled it right. So, one can say he forgot to account for spindrift or despite his excellent shooting he has a habit as must right handed shooters do, of pulling right.

target size, well they vary, but will tell as most can attest, I have two out of 3 targets on the Rifles Only 1000 yard berm which measure 8.75" X 14.75" and I use that to practice on... however I also use a Larue, which is 11.75" which with a value of .75" MOA dialed in, or should say not dialed in would result in a miss if I did not include it. I must be so talented to always blow my wind calls in favor of not using SD instead of the other way around. As far as ASC, I don't have all the target sizes in front of me. The Raton Sporting Rifle Matches hover around 1 MOA or less.

 

[Lowlight]

Re: Spin Drift

This type of shooting, as with any competitive sport attracts A type personalities so those with a thicker skin does prevail.

i don't dont see the issue, but then again, the issues may have been pointed to me, in which case I wouldn't.

 

[USFTR]

Re: Spin Drift

I think we are saying about the same thing, just in different ways. As a general rule, we are trying to attract people to the shooting sports. Yes, it is advisable to have a thick skin, but does that help our cause? Do you want to turn people off from shooting your sport? If you do, then we have more people going around that are ok with a ban on "sniper rifles" because they don't shoot a rifle. Please be careful how you interact with people, especially if they are asking a question because they don't know the answer. Politically, we need people on our side.

With respect to spin drift, I think we both agree it is small and 95% of the time, probably will not be noticed by the shooter due to body position, trigger control, and especially the wind. Why do you not account for this and still have first round hits, probably due to the size of the target. I'm trying to hit a 5" bullseye at 1000 yards, so a drift of 3-6" from my 200 yard zero is meaningful. I see you have "Base of the Rockies" as your location. That's probably why you don't see as many true no wind moments as I do on the east coast. I rarely see them, but they do occur and that's when I see the drift.

I'm not trying to stir up anything, but I truly believe some of what he is seeing is due to spin drift. At 1000 yards, 10" spin drift seems excessive and so yes, trigger control or wind is probably another factor. So can we at least agree on what I have said and let this topic die?

 

[Lowlight]

Re: Spin Drift

Well I am not going to apologize for anything I said here, I see no reason for it. You can fall back on the banning talking points, but the fact of the matter is, more people feed into myths and legends and lead people down a false path rather than being honest and telling someone they are screwing up the fundamentals. So if honesty is a problem, then I am guilty. Too often people let others simply shoot, when they are supposed to be instructing and overlook obvious errors in form or execution. I chose to hammer down on shooter, and not focus on what may or may not be issue. As Sterling is fond of saying and I agree with, recoil is angular, and just because a fixture experiences one set of effects, doesn't mean those effects translate the same when a human is behind a rifle. I know for a fact that differences are seen even by the guys who have run the doppler tests, I have been told in person so. The fixtures tell one story, people tell a different one.

And I think I am bit familiar with F Class, and have shot a match or two here in Raton, so I understand the "target" issue. You're X ring is only one component of the entire target. I can tell you this, I would be willing to go out on a limb here and say you are probably shooting a 8-32X scope, maybe as high as 42X, and that your quartering a very large target hoping to bring them center. So the idea you are cold shooting a target in F class isn't exactly the same. you get sighters, you get spotters on the target, you have coaches, wind flags and known distances that point to a 4ft number block behind a 6ft square frame. Here, things are slightly different. The reticle covers anything that small especially at 800 yards and beyond. Granted many are now making cross over scopes and reticles that are somewhat like the NF, very thin, but still, your average tactical scope cannot see a 5" wide target and I am very sure you are not first round hitting center on something that small. Besides you have dope for the yard lines you are shooting. You're going for it sure, but be honest, the 10 ring is nice too. You're not complaining about missing center if you hit a 10. An 8 is disappointing, a 10 is every bit as important as the X.

I have dug up targets and can show you an 800 yard target that started with two rounds on steel where i transitioned to a paper target because someone on here claimed to be shooting a 5" Shoot N C at 800 yards. I wouldn't see the 5" target behind the reticle, but managed the next 3 nicely in the black, and my cold shot and follow up where just slightly left of center when I figured the wind. Adding for drift would have been a miss, plain and simple the calls were well placed from the start. So should you want to see them, I have them available.

The entire system plays a part of it... is the scope tracking true, is the shooter simply focusing the parallax knob or actually understand and adjusts for true parallax and not just image focus, this stuff matters much more than adjusting for SD.

yes it exists, yes it has value, but only when all things are perfect. Clearly by the number of targets we see posted on here weekly, many, many shooters, including myself have much more to think about even at 100 yards then to worry about SD inside 1000. if it works for great, it doesn't work for me no matter how they model it.

 

[The Mechanic]

Re: Spin Drift

You must not be very busy Frank. This is the most posting in one thread by you I have ever seen. Usually one post on Coriolis, or spin drift and that's it. But I must say I am enjoying it. Time for a book. If Plaster can do it so can you.
Chapter one. Spin drift, lunar drift, and Coriolis.
Chapter two. Helo shootin' movers.
Chapter three.....