Wind and it's affects?

[Mikecr]

there are several BC's that must me taken into account to accurately project where the projectile will eventually end up

This again is better another thread, because there ARE NOT multiple BCs for a given bullet. There is one true BC.

Sierra knows the true BC, but it does no good to provide it because our software does not utilize Sierra bullet drag coefficient curves. We use the G1 standard... So as a workaround, and to potentially provide corrections to weak software out there, Sierra provides adjustments.
Adjustments that likely screw us up more than anything..

Bryan really did the same with Bergers by averaging G1 adapted BCs over downrange values.
He did this to 'help' us, but it's bad science.
So there is a scary trend of simplifications & generalizations to better serve us, that skirt truths.
And to account/discount for these actions correctly, we must understand matters for ourselves.
For example, we must recognize that the 'easier' Miller stability formula is a rule of thumb only that does not represent all real truths. It will fail tests, and there is no particular reason that stability SHOULD be so easy.
So this leaves us with far more difficult McGyro math to understand.
It's on us to do so, or not.

Potential discussions for other threads..

 

[Boss Hoss]

Mike---The scientist at Sierra (can't remember his name) who has actually developed this data in the tunnel in Missouri is correct in at least the predicted trajectory of the bullet because I have checked it. Now this was only at 500 yards but it was less than .5 off and my group that I used to check it had a 9fps spread and were fired within 2 minutes so the temp was the same. Used my LV competition rifle to verify this.

 

[Mikecr]

Oh I know Sierra folks know their stuff.
Providing you with a working trajectory is cake walk for them(and many here).
But Sierra didn't have to use 3 BCs to get-r-done, and neither would we. They can use the actual BC, from the actual drag coefficient curve, which they produced in the tunnel(that's beyond any of us).

If OUR software included and referenced Sierra bullet drag curves, they could provide us with a single - actual BC, without fear of us running from the lower number they provide!
That number would be near, but not, G7 BC.

 

[groper]

Ok this is great, now im beginning to understand why i may have missed some of those shots that left me scratching my head.... i may have had it all backwards from day one....

so to clarify a bit further, i want to know more about this 'time lag' and what exactly it is?

So far i can see an argument that when a bullet exits the muzzle its drag is highest due to highest velocity. i know drag is proportional to velocity squared. so would it be correct in saying that the wind deflection is in some way proportional to the bullet drag or is it something to do with deceleration?

 

[Pdvdh]

Time for some research:

http://www.exteriorballistics.com/ebexplained/articles/article2.pdf

I haven't completed this read yet. Pretty darn technical. The Sierra guys admit to error in their original article and intend for this one to correct it. I read enough to understand that much.

 

[groper]

thankyou phorwarth, an interesting read. i now understand why the wind has more effect at the muzzle now.

From the sierra reasoning, it would seem to me that the muzzle or 'near wind' has the greatest effect because the bullet aligns its axis with its "trajectory relative to the air" which of course is at a slight angle compared to its trajectory "relative to the ground". This makes sense, and you can observe this phenomenon when a aircraft lands in strong crosswinds, they come in a little sideways.

Then, if the wind direction were to change further down range, the bullets axis or angle has already been established at the muzzle and already causing drift velocity sideways, the gyroscopic forces of the rapidly spinning bullet resist significant changes in drift until the angle of the bullet can realign itself with the new wind direction.

I also got this out of it.... if your shooting long range in a strong crosswind from left to right, add an extra click of elevation. If your shooting in a strong crosswind from right to left, subtract 1 click of elevation. Happy days

 

[bigngreen]

This is turning into a great thread, I have always tried to see what the wind was doing near my target, I haven't really been doing anything with it other than seeing if it may give me a clue as to what is happening. I'll work on focusing on clues closer to my positions, I think I have been over looking some important clues!

I'm trying to get into understanding the numbers but I just am not able to, you could through a pile of junk in the middle of the room and give me a hammer, electrical schematic, and a crescent wrench and I'll build a combine or tractor out of it but write numbers on paper and say they do something and I'll have smoke coming out my ears, but I'll give it a try.

 

[Boss Hoss]

This is turning into a great thread, I have always tried to see what the wind was doing near my target, I haven't really been doing anything with it other than seeing if it may give me a clue as to what is happening. I'll work on focusing on clues closer to my positions, I think I have been over looking some important clues!

I'm trying to get into understanding the numbers but I just am not able to, you could through a pile of junk in the middle of the room and give me a hammer, electrical schematic, and a crescent wrench and I'll build a combine or tractor out of it but write numbers on paper and say they do something and I'll have smoke coming out my ears, but I'll give it a try.

hehehehehehe-----learned this years ago from Speedy as he always told me everyone would watch him put his wind flags up! He only used a couple out close ones of 6 or so.....

As I said in the other thread----what is happenning 3/4 down range is of little interest to me compared to the first 1/2.

Just don't let the people I shoot against for score read this!!!!!!

 

[Mikecr]

Ok, I believe I've managed to assemble an incremental drift chart that demonstrates the affects of near wind -vs- far wind.
You'll notice that hitting a 10mph wind within 100yds is significant(~1.5moa by 1kyd including 50yd + 100yd drifts), even without further downrange wind. You might also notice that ~1.5moa 1Kyd deviation prints under .5moa at 100yds.
How can this be?
Because drift is not a linear minute of angle path, but a non-linear curve. Much of that ~1.5moa deviation occured WITHIN the first 100yrds, and therefore does not apply to the full first 100yds.
It will apply in the next though...
Anyway, I doubt it's perfect, but lend me 30 IQ points and I'll make it so.

By null at 2010-08-22

 

[bigngreen]

Thanks Mike!! That's the kinda of presentation that a guy can start to wrap his mind around!!!

 

[Pdvdh]

You'll notice that hitting a 10mph wind within 100yds is significant(~1.5moa by 1kyd including 50yd + 100yd drifts), even without further downrange wind. You might also notice that ~1.5moa 1Kyd deviation prints under .5moa at 100yds.

Can you provide the exact numbers from your Table, so I have a better chance of following your discussion. Which two numbers are you adding to get ~1.5moa by 1Kyd?

And where do I look to see that ~1.5moa 1Kyd deviation prints under 0.5moa @ 100yds.

I'm struggling to follow your narrative.

? Why don't the values in the fourth column match the values in the 2nd column? Why the ~15fps difference?

 

[Mikecr]

I'll describe the 10 columns, to hopefully answer your questions.

- COLUMNs 1-3 are are part of a baseline solution provided by a Pejsa spreadsheet from input parameters to the far left(MV3000, BC.500, etc)

- COLUMNs 4 put my mind in a ditch initially. I needed a representative velocity throughout each 50yd increment to determine incremental LAG.
The velocity shown to drop to 2901fps by 50yds in COLUMN2, does not represent what velocity was through the first 50yds, but only what it ended up at.
'Effective velocity' was somewhere between 3000-2901 for that 50yds, and yet was not simply the halfway point(non-linear change).
So I started with a simple avg, and added again a percentage of the average, to the average, to roughly balance the checkbook(*I'll followup on this at COLUMN 10).
You noticed 15fps diff early, but actually it gradually ends up 13fps diff downrange. That's because averages spread downrange(slower loss rate).
With this I'm confident that the velocities in COLUMN4 represent the effective velocities well enough for each -50yd increment -for these velocities -& BC.

- COLUMN 5 shows the incremental velocity drop w/resp to original MV(VacVelDelta).
- COLUMN 6 just shows COLUMN5 as percentages.

- COLUMN 7 shows incremental T-LAG based on the ROW6 percentage of time added(inverse of dropping vacuum velocity)

- COLUMN 8 shows incremental path deviations caused by a 10mph crosswind. This is WIND*T-LAG at each 50yd increment(not summing)

- COLUMN 9 converts COLUMN8 deviations per 50yd to MOA

- COLUMN 10 brings it all together. Each row shows the individual 1kyd drift contribution, of a 10mph crosswind, produced at each range increment.
The bottom cell sums the contributions for total drift at 1kyd.
*The correction applied to effective incremental velocities in COLUMN 4, allowed COLUMN10 TOTAL to match the original solution.
It's not dead nutz, could use a bit of exponential, but provides for overall accuracy.
So please don't take this too literal. It's merely an effort towards general understanding of the impacts of near to far winds.

Phorwath
The ~1.5moa at 1kyd = COLUMN10 50yd + 100yd deviations
The ~1.5moa at 1kyd -value printing at 100yds = COLUMN8 50yd + 100yd deviations