Spin drift: Why do people say it doesn't matter?
- Thread starter Roddy
- Start date
Most people at PRS matches are using ballistics calculators and calculating their dope prior to the stage. Good ones like AB mobile can add the spin drift to the solution. So there is no extra effort needed to use it. In the end it will come down to your wind estimate...
Find it strange that people worry about spin drift but not about aerodynamic jump...
Find it strange that people worry about spin drift but not about aerodynamic jump...
I guess people have been aware of spin drift for longer than aerodynamic jump? Plus it's way simpler to apply than aerodynamic jump. I admittedly don't factor aerodynamic jump into my firing solution at matches cause I basically use my ballistics calculator to give me my elevation adjustment at range as well as a wind adjustment at that range for a fixed value (10 km/h). Since the wind never seems to be stable in Eastern Washington, I use my Kestrel during the stage prep time time to get a feel for what the max and min values are and apply that to my 10km/h wind value when I'm at the line. I guess I could hold up or down from my baseline elevation depending on wind strength, that's a lot to think about...
Spin drift for my average conditions is 5.3" @ 1000...
Kinda hokey to not take into account coriolis as its 8" @ 1000
Or at least aknowledge that you are mashing spin drift and coriolis into a single number
Here is a chart showing what is really going on, the center row is for 60f 3238fps 105 amax 28" of mercury 1-8 twist
Ps horizontal coriolis is always full value regardless of which direction you are facing. Poi to the right in the northern hemisphere
Id be impressed if someone turned on their brain and made barrels with a left twist for us north of the equator so coriols and spin drift sort of canceled each other out
Kinda hokey to not take into account coriolis as its 8" @ 1000
Or at least aknowledge that you are mashing spin drift and coriolis into a single number
Here is a chart showing what is really going on, the center row is for 60f 3238fps 105 amax 28" of mercury 1-8 twist
Ps horizontal coriolis is always full value regardless of which direction you are facing. Poi to the right in the northern hemisphere
Id be impressed if someone turned on their brain and made barrels with a left twist for us north of the equator so coriols and spin drift sort of canceled each other out
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Gunnerlove
CGN Ultra frequent flyer
- Location
- Vancouver Island
Not that I spent much time in the Artillery but that makes no sense to me. The Earth always moves East, so the Shell will always drop West of where the Tables and Bearing say it should.
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Theres no doubt about it, its always poi to the right. Get a globe and set a firing point and a target, pretend to fire at your target and spin the globe an inch, pay attention where you actually "hit"
Remember for east/west shots you are leveling your rifle perpendicular to gravity at your particular lattitude not perpendicular to true east/west which is only at the equator
This video helps understand, but for it to truly click I needed to play with a globe
https://m.youtube.com/watch?v=K8TEj4WeHuk
Or you could just blame the wind lol
Remember for east/west shots you are leveling your rifle perpendicular to gravity at your particular lattitude not perpendicular to true east/west which is only at the equator
This video helps understand, but for it to truly click I needed to play with a globe
https://m.youtube.com/watch?v=K8TEj4WeHuk
Or you could just blame the wind lol
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Hmmmm,
I never knew the correct name for this.
"Aerodynamic jump"
I've seen it for years and know to compensate, just never knew what it was called.
On my rifles wind from the left cause low impact
Winds from the right cause high impact.
Kind of a 10 o'clock to 4 o'clock thing.
Speed of the wind determines how much high or low.... in addition to the obvious leftage or rightage.
In a string based event like F Class, you will learn to spot this and learn to adjust for it fairly quickly once recognized.
It would take a real proactive mindset to actually factor this in in real time in a PRS match. It gets well into cognitive overload.
I'm not even sure that honestly in practical terms under the clock, that it could actually be done in PRS, given the typical 1 round and move format.
Wind can and does change in an instant, so getting the output from a ballistic calculator before you start shooting would have limited value after the wind shifts 10 seconds later.
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Magnus effect.....
There's a great video on SH that goes into aerodynamic jump. They also go into it in the vid about Hornady's new 4DOF ballistic solver. As far as Coriolis, my understanding is that inside 1k yards you can't even adjust for it, it's something like 1/10th of a mil with a .308 doing 2700fps @1000 yards
No, it just takes being proactive in creating your dope cards for stages. One of the things that was also apparent at the Meaford match was that data management was a weak point for many people new to PRS.
Savy PRS shooters create stage specific card that focus the data they need but allow them to adapt it to the conditions quickly. A savy shooter will put wind hold values on their sidewinder/wristcoach cards either for the estimated wind value bookends or two specific values like 5 & 10 MPH (for each distance). If they want spin drift, just enable it in the ballistic calculator and its included in the solution. This allows them to make better wind estimates at each distance using the previous shot. Since most use FFP, they know what the wind hold was for the distance they just shot and can look at their cards and interpolate it quickly for the next distance and adjust for angle (easier to do with mils than with MOA on the fly).
Aerodynamic jump isn't something people would factor in unless it was a prone stage with small targets (TX match I just went to had 1 MOA targets on all prone stages which went out as far as 1160 yards). To use it, you just put your elevation as a range or put the difference of the aerodynamic jump as a superscript or subscript on the elevation value and hold for it with the wind.
Example sidewinder card:
Each distance has raw elevation (hold over/under strategy) 5 MPH hold 10 MPH hold.
If I wanted aerodynamic jump I would be dialing for sure and would use hold over space for that info.
Peter we both said this.... after a conversation with Kombayotch we found that there is too many cross references that contradict each other and mearly confuse people and with the new testing and findings these terms can be more defined to what they are with no grey area and confusion as old findings are being debunked and found untrue.....we were both right on the Magnus effect call..... applied ballistics solvers do account for aerodynamic jump as well as Magnus effect, not sure if Atrag does or not.
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Hmmm... So...
Guys in PRS are trying not to get DQ’d over a safety violation while transitioning from one dusty gritty gravel laden position to another without their bolt open or flagging someone or pointing their rifle too high while positioning themselves on deliberately awkward support obstacles, and transitioning across a series of 6-9 targets in the right sequence in 90 seconds at various distances outside 300 yards and then take the time out to simultaneously assess the current wind speed and direction, make the wind call and look at their cheat card to factor in magnus or jump or whatever you call it adjust their scope, aim... wobble a bit... aim a little better and shoot.
By the time you do all this, you might get 2 out of your 8 shots off before the buzzer goes off regardless of how well prepared your documentation may be.
The reality is that you’ll make your best wind call seconds before your name is called and that is the wind call you will use throughout your stage. More than likely the wind will have changed several times by the time you actually start breaking off shots. You will be focused on running the stage as best you can. The last thing you will be thinking about in those 90 seconds is this thread.
Understanding the subject has value, no argument... more so for f class
Filtering out the noise and getting down to what you can realistically apply in the time allotted without frying your brain is about the best we can do.
See also paralysis by analysis.
Guys in PRS are trying not to get DQ’d over a safety violation while transitioning from one dusty gritty gravel laden position to another without their bolt open or flagging someone or pointing their rifle too high while positioning themselves on deliberately awkward support obstacles, and transitioning across a series of 6-9 targets in the right sequence in 90 seconds at various distances outside 300 yards and then take the time out to simultaneously assess the current wind speed and direction, make the wind call and look at their cheat card to factor in magnus or jump or whatever you call it adjust their scope, aim... wobble a bit... aim a little better and shoot.
By the time you do all this, you might get 2 out of your 8 shots off before the buzzer goes off regardless of how well prepared your documentation may be.
The reality is that you’ll make your best wind call seconds before your name is called and that is the wind call you will use throughout your stage. More than likely the wind will have changed several times by the time you actually start breaking off shots. You will be focused on running the stage as best you can. The last thing you will be thinking about in those 90 seconds is this thread.
Understanding the subject has value, no argument... more so for f class
Filtering out the noise and getting down to what you can realistically apply in the time allotted without frying your brain is about the best we can do.
See also paralysis by analysis.
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Like most anything that involves skill, it only really matters, when it Really Matters. To be at your best when it's time, it has been my experince that preparation is the key to success along with a huge dose of mental readiness. To me one strengthens the other.
Besides in any competition, I strive to make others beat me, not to beat myself and for me, being prepared helps that.
On the drift topic, if you can live with a couple inches left early and a couple inches right at 1000, maybe zero around 700 and call it ok.
Besides in any competition, I strive to make others beat me, not to beat myself and for me, being prepared helps that.
On the drift topic, if you can live with a couple inches left early and a couple inches right at 1000, maybe zero around 700 and call it ok.
As has been mentioned before, the only time anyone would really need to account for something small and variable like aerodynamic jump in a match is prone on small targets. If you're shooting off something awkward, targets are in the 2 moa range. You won't miss on account of aerodynamic jump. If it was a constant value like spin drift that you could just plug in, then hey, why not.
As for making your wind call seconds before you get to the line, well that depends if the wind has been at all constant. You'd normally get a max and min value for the wind while waiting for your turn and try and correlate that with visible signs or how it feels on your face, etc. I normally know what I'm gonna hold for wind as I get to the line but I'll amend that hold when I'm in position if I've felt/noticed a change. Either that or I'll correct on my second shot, haha
You have that perception because you are new at it and things seem overwhelming. Everything is a conscious effort as little is automated in your subconscious. Most of that goes away as you gain experience, and it does more quickly if it is part of your training routing. With time and training the safety stuff isn't something you think about consciously on the line. Opening the bolt before you move, finger outside of the trigger guard, muzzle down range. If you make these part of your practice sessions, they becomes muscle memory and are controlled by your subconscious. You don't need to think about them on the line. No different with experienced IPSC or IDPA shooters. Safety stuff gets automated with practice. Same goes for building a stable position, the techniques get automated with practice. Marcus talks about that in his book in the thread below.
You're also thinking about the ballistics too piecemeal. Get a sidewinder or Hawk Hills dope card holder so that your data is right in front of you nose and you don't need to break position to look at it. If your card is prepared properly, you don't need to think about anything in this thread. Your spin drift is already rolled into the hold-off numbers and they are adjusted for shooting direction before you're on the line. Use the feedback your reticle gives you (FFP is your friend, so are mils). Measure the wind when you're not shooting, watch the dust of the impacts of the shooters on the line. Figure out the the bookends of the conditions on the range are. I like to use 5 and 10 MPH wind values on my cards. Many guys will put the values for the bookends they are estimating. Doesn't matter as long as they are the same wind magnitude for each distance. Two numbers for elevation (if you want to incorporate aerodynamic jump), two for wind for each distance with the pertinent stuff rolled into them is all you need. For both elevation and windage, first number is for one bookend, second numbers is for the other. Interpolating the number is easy with the small mil numbers. Your wind assessment can often be based on your previous shot, particularly if the targets are in a troop line as they often are. If T1 required 0.6 mils, a good estimate for T2 is 0.7 mils on the card above. It's a much better estimate than holding off "yeah about that much" at the next distance. Adjust for the changes in mirage and vegetation you are seeing. Break wind direction into clock values. You have full value, none, half at 1/5/7/11, 3/4 at 2:30/4:30/8:30/10:30 and 90% at 2/4/8/10. Your dope numbers are rounded to the nearest 0.1 mil, so the multiplying numbers don't have to be the exact COS/SIN values for those angles.
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