# Wind and it's affects?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by bigngreen, Aug 20, 2010.

1. ### bigngreenWell-Known Member

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From another thread that started as a total other subject! Are our bullets pushed by the wind or what and what is more important and has more effect in regard to reading the wind, wind at the shooter or close to the target? Lag time vs Time of Flight? Hopefully I don't breach some internet forum protocol doing this!

The starting thread http://www.longrangehunting.com/forums/f19/new-software-development-request-60049/ the questions start in pages 4-5.

Mikecr
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Re: New Software Development Request
Quote:
Originally Posted by groper
Mikecr, take a 1200yd shot for example... using my .308 and using my ballistic calc, my bullet flys thru the first 400yds in approx 0.49 secsonds.

From 400yds - 800yds, the same bullets takes 0.65 seconds for this middle leg.

And the last part of its flight from 800 - 1200yds, it spends a whopping 0.90 seconds. Total flight time = 2.04 seconds.

So it takes almost twice the time to complete the last 1/3 of its flight compared the the first 1/3. This means whatever wind is present during the last 1/3 has almost twice the time to apply its vector and drift acceleration on the bullet.

Furthermore, as the bullet slows down its BC decreases, so in the last part of its flight it not only has to be effected by the wind for longer but the wind can push it more easily due to a lower BC.

Ok, a few problems with this argument;
1. It's probably better for another thread
2. Wind doesn't 'push' bullets anymore than rain 'wettens' bullets. With this, wind calculations are not based on TOF, but instead on TIME LAG. And these calcs can be performed from yard to yard as well as muzzle to target. YOUR argument suggests that very heavy bullets would drift more in a given wind because their TOF is higher due to lower MV. This is not true -because their lag time is lower, because their BC is higher. Heavy higher BC bullets, launched slower, drift LESS given enough range to demonstrate. And the majority of their drift(in moa) still occurs right where lag time is highest(nearest the muzzle).
3. Actual BC does not decrease as a bullet slows.
The changes in BC you notice result only with comparing actual/local drag coefficients to G1 or G7 standard drag coefficients. This is neccessary for software that makes this comparison. Not so with software that doesn't. I assure you, with your bullet's ACTUAL drag curve referenced by your software, BC would remain constant with velocity. Pejsa manages this feat with a coefficient adjustment.
As well I'll assure you that drag itself decreases with dropping velocity.

groper
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Re: New Software Development Request
1. im fine with another thread, until then it stays here.

2. when its windy, my bullets get pushed. When it rains, my --- gets wet. I dont understand what your saying here?

The wind imparts a vector on your flying bullet same as wind imparts a vector on my aircraft when i travel from one airfield to the next. gravity imparts a vector on it in the same way also. There are 3 parts to these vectors... direction, force, and time. When i say time, this is the amount of time the force is applied. so in the case of windage the time the bullet spends in horizontally moving air not including any time of its journey spent in still air. With gravity, its the entire time of flight obviously.

3. What is time lag? ill take a guess and say that perhaps you are referring to INERTIA? In that, it takes more force to accelerate a heavier bullet than a lighter one, everything else being equal. Thus a heavier bullet drifts less in the wind. i totally agree with this, but heres the thing.... what happens when you have 2 bullets with the same WEIGHT, but one has a much higher BC than the other? Which one drifts more or less and why? Obviously, it has to do with the form of the bullet not just its mass.

I still dont see your point with regard to time lag???

Last edited: Aug 20, 2010
2. ### EagletWell-Known Member

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Lag Time is the difference between the actual time of flight and the time of flight in a vacuum.

Vacuum meaning the time the bullet will take to travel the same distance without any air resistance.

Last edited: Aug 21, 2010
3. ### groperWell-Known Member

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No, you are getting 2 different things confused here... for example, by your argument, if you launch a bullet slower then you will have less drift...see?

what happens when you launch the same bullet, same bc, same distance but at a much lower velocity so the TOF is longer? do you get more or less drift? explain that...
ok so explain why when i shoot in 10MPH 3oclock wind @ 100yds i might need say 0.1MOA wind, and in the same wind 10MPH, 3oclock conditions @ 1000yds now i need 6MOA... thats 60 times (the MOA) adjustment.

And thankyou eaglet for showing me what lag time he was referring to... i notice in the explanation of it, 2 things that effect it are muzzle velocity and BC. Therefore its worth noting that a lighter bullet can have a much higher BC than a heavier bullet, and therefore a lighter bullet can have less wind drift than heavier bullet.... therefore bullet mass is not worth discussing any further.

Last edited: Aug 21, 2010
4. ### bigngreenWell-Known Member

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Here's some gas for the fire Loadbase 3.0 using multiple winds set for 10mph and correcting for a 1000yrd shot. Correction for wind at the first 200yrd and none the rest of the way is 1.6 MOA, correction for no wind till the last 200yrd is .4 MOA. It would seem that the wind in close has the greater net effect.

It would seem that a miss call on windage in close will have a greater effect at the target than a miss call closer to the target. Using my 270 WSM for an example.

5. ### groperWell-Known Member

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And one more thing, whilst i remember it.

When i fly an aircraft from one airfield to another, lets say for simplicity these 2 airfields are 100nautical miles apart and are due north south from each other. My aircraft will fly at 85kts.

There is a 30kt wind blowing from true bearing 45degrees.

after 1 hour, if i pointed due south, i have a ground speed of 100kts due to the crosswind 45deg up my --- and i get blown off course 15miles west of where i wanted to due to the 45deg cross wind. i find the airfield to the east and land.

Now, i want to return home in the same wind conditions and this is where it gets interesting....

Again, if fly due north at airspeed 85kts, everything the same except now im pointing due north instead of due south, will i arrive at my home airfield 15miles due west of it like i did when i flew south?

Why?

6. ### groperWell-Known Member

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I see why, the angle is changed over a greater distance ie 800yds instead of 200yds. This is something i didnt stop to consider...

What happens when you input 10mph wind left for the first 500yds and 10mph wind RIGHT for the second 500yds?

7. ### EagletWell-Known Member

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In Bryan's book, Applied Ballistics for Long Range Shooting, has an awesome explanation on this theme. The whole chapter 5 is devoted to Wind Deflection.

Bryan talks about "near wind" (at the shooter) and "far wind" at the target and explains about reputable proponents of both claims.

In his explaining he calls "strike one" to the near wind proposition, "strike 2" to the far wind proposition, and even "strike 3" for the in-between wind where the bullet will have its highest path where the wind will be more active.

I can only say it's some cool reading on the subject and you owe it to your self to get the book!

I don't how much can be said without hurting his work, but I'll tell you there are five things helping my long range shooting.
A) My Swarovski LG range finder
C) Bryan's Book
D) My 338-300 RUM in savage action "put together by geargrinder" which today at 673 yards busted a coffee lid from McDonald's on the 2 shot. The first shot would have killed anything else.
The last, but not the least, is LRH site!!!

Last edited: Aug 21, 2010
8. ### bigngreenWell-Known Member

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At a 1000 yrd I get 1.9 MOA left, the earlier wind has a greater effect. I ran it out till they evened out and it was just under 1300yrd, with wind the whole way from 500yrds. So it took 800yrds of right wind to move the bullet back to center from what happened in the first 500yrds of left wind.

9. ### bigngreenWell-Known Member

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I still haven't got Litz's book, I need to get it bad. I had it in the cart but I got a vid on chambering competition barrels instead. I'm realy torn between buying stuff that helps me shoot better and buying stuff that I can make bigger, better, longer shooting rifles with

10. ### MikecrWell-Known Member

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Bryan did not take sides in his book. Wind is a relatively small discussion there.

But formulas in his book support my contention that wind's affect is applied directly to LAG, and NOTHING else: "Actual wind deflection is directly proportional to time lag and crosswind speed" Applied Ballistics, p68.
Wd = Ws * Tlag

Wd =wind deflection
Ws =crosswind speed
Tlag =lag time in seconds = TOF - TOFvac

Now lag is not directly about velocity, or bullet weight, and that is not the context of my near wind argument.
LAG IS CAUSED BY DRAG.
And I would think ANY portion of total TOF to LAG within it, must be considered to understand wind drift.
Afterall, the truth passes all tests.

11. ### Boss HossWell-Known Member

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Also --- all wind values are the same for this.

muzzle to 300 yards 8'oclock condition, 600 yard flag 10'oclock, and 1K berm 9'oclock

Now on this bullet a 142 6.5 SMK there are several BC's that must me taken into account to accurately project where the projectile will eventually end up plus remember:

Where will the impact be???? MV is 2945fps

Last edited: Aug 21, 2010
12. ### SHRTSHTRWell-Known Member

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Hi,
I am glad to see this thread materialize. I have been following several other threads that somewhat pertain to this one. I have a couple questions I would like to straightened out on.

Eaglet posted a Youtube video of a segment on BOTW. I watched this show about a year ago. In this segment they explained that you should point your wind meter at the intended target, as this is the actual wind the bullet will encounter. This makes sense but I wrote it off, figuring their setups were different than what we do here on LRH.

I have been using my Kestrel to find out what direction the wind is coming from and put this info directly into my PDA. Example: Lets say I have a 10mph wind at 9 O'clock from my intended target. I have always pointed my Kestrel at 9 O'clock and put 10mph in my PDA.

If I understand correctly what BOTW is doing. They find out which direction the wind is coming from and then point the wind meter at the intended target and use that wind reading for their firing solution. Could someone explain the correct way to do this for me?

I am in the fireforming process of a new build and almost ready to start load development on fireformed brass. I have Exbal and Mobal ballistic software and am most familiar with Exbal. I do not care for the PDA that comes with Mobal but know a couple guys that swear by the ballistics program.

I just purchased another Ballistics software program from "Len" this morning. I figured that since I am about to learn my new rifle...I might as well learn with new software capable of using G7's and account for Spin drift and Coriolis and different winds. Just another gadget .

So, I have to ask this question. When using some of the more sophisticated ballistic progams offered today....how cumbersome are they in real world hunting conditions. In other words, when that trophy is 1000 yards out and the adrenaline is pumping...how long does it take to get a firing solution? I am sure the more experienced an individual is with his equipment the faster he will be at getting it done. Just curious how you guys handle this in the field.

Just trying to learn here guys, hope this makes a little sense. By the way, I tried not to use the "L" word .

13. ### Boss HossWell-Known Member

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When I am shooting in a match the muzzle to 300 yard condition is given the most consideration followed by the 600 yard condition. The 1K Berm I seldom use.

14. ### Boss HossWell-Known Member

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AHHHHHHHHHH Young Grasshopper-------That is the final stage of enlightenment. It is not an easy task however, learn to read condition and you will be rewarded. The PB Software I just got is rather HAS PROMISE!!!!!!