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So how does wind effect the DRIFT direction of a pellet?

January 31 2007 at 10:04 AM
Greg S  (Login gks3)
YFOT

It’s driving me crazy. I have been trying to get a handle on wind drifting and its relation to a pellet with not much success. Lot of info on what’s makes the biggest difference but not much on "if the wind blow this direction your pellet will do this".
I understand the twist direction of the pellet has an effect (rifleing).
I swear that when the wind blows behind the pellet, it drops its POI. When the wind blows at the left side of the pellet (left to right) it pushes it right AND drops the pellets POI.
I am using 2 wind flags, one at 10yds and the other at 40yds with the target at 50yds. Winds being 7-10mph with 15mph gust. Wind usually blowing up the pellets A$$ but also a lot of "snaking" winds and 90 degree to the left side of pellet. Velocity 913 with .177 JSB 8.4gr weighed. Here’s a pic of my situation:


For those that recognize the pic, yes I finally have a new gun. Posts on that later.

So is there a chart like the pistol pie chart that shows what you may be doing wrong do to POI and how you grip the pistol/rifle?
One that says "pellet will go here if wind blows from here and only to this extent", 2 of them of course based on direction of rifling.

Also, are these effects relevant to pellets the same as bullets, all other things being equal with the exception of design of course?
Any input would be greatly appreciated as long as it’s factual and not "what makes sense". Thanks.



greg in WA

 
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AuthorReply


(Login DonMatzeder)
YFOT

My experience

January 31 2007, 10:20 AM 

is that they are the same..


Take my advice, I'm not using it anyway.

 
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(Login gks3)
YFOT

Thats is exactly what I am talking about.

January 31 2007, 10:30 AM 

Thanks again. This is perfect.

greg in WA

 
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Yrrah
(Login Yrrah)
YFOT

My real world experience with air rifle pellets is not in accord with Don's diagram.......

January 31 2007, 4:08 PM 

Don and I have had a friendly running discussion on this for some time. There are a number of possible reasons for the lack of agreement. One possibility is that Don's information and experience may be related to bullets which have their centre of wind pressure forward of their centre of gravity and air rifle pellets generally are the reverse. In any case here are the real world effects of right and left hand winds on my points of impact at 100 yards with JSB Exacts:

The string of shots impacting to the right of the target centre ( and POA ) were shot in a left to right wind which was varying in strength. They have struck to the right of the POA and higher than the POA which does not fit Don's model for any wind from any direction. The tight group to the left and low was aimed at half way between the target centre and the 3 0'clock edge of the target. They were deliberately shot in a strong right to left wind and released when it was deemed that the wind flags were showing consistency from shot to shot. They have struck low and some 10 inches left of their point of aim. This does not agree with any wind from any direction in Don's model.

[IMG][/IMG]

Here is another target shot in a right to left / left to right (edit)wind on a different range which was in fact at 90 degrees to the one in the exhibit above. It was shot in a following wind that was fishtailing from 4:30 to 7:30 or so. There are two groups one below the other ( with a sight elevation change for the lower group ). The pellets shot when the wind was from the left have impacted to the right and high and those shot when the wind was from the right have impacted left and low. This is not in accord with any wind effect on Don's diagram.

[IMG][/IMG]

I can only describe my real world air rifle pellet experience and the evidence to support it. If in fact it is a quirk of my ranges and at another time on another range things reverse then I shall report that too.

In respect of your pellets dropping lower than expected in a following wind: It is quite common when there is a building directly behind the shooting line. The air rushes over the building and then down pushing the pellets down as they pass into that downward draft. .......

Nothing is simple and you may just have to get to know your range which has many trees and the building to cause complicated swirls that are perhaps more deviant than that situation on a more open range (edit)....... With respect to Don and all other readers whose experiences and opinions may differ from mine...... Kind regards, Harry.





    
This message has been edited by Yrrah on Jan 31, 2007 9:15 PM
This message has been edited by Yrrah on Jan 31, 2007 9:10 PM


 
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(Login DonMatzeder)
YFOT

I have a theory

January 31 2007, 4:39 PM 

that the difference is in that you live in the southern hemisphere ;^)

Take my advice, I'm not using it anyway.

 
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Yrrah
(Login Yrrah)
YFOT

When conditions are suitable I will endeavour to do a head to head

January 31 2007, 5:40 PM 

between my air rifle and my rimfire alternating shots between the two at 100 yards. If you have a .22 PCP and some heavy headed pellets that suit it ( Exacts and Kodiaks come to mind and not much else ) then you may be able to do the same to compare notes down the track? ...... You think The Southern Cross may hold the answer :>) ? ...... Kind regards, Harry.

 
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(Login DonMatzeder)
YFOT

The most difficult part

January 31 2007, 6:07 PM 

is finding switching winds consistent enough to get a "true" zero. I shoot many matches knowing I am not truely zeroed, but it is not required as long as you get repeating conditions. Shooting from day to day to get different wind also gets you different barimetric presure and humidity. Shooting at home skews results too because I shoot on enough of a hillside that there is a vertical component to the wind as it follows the contour of the ground. There is a level, open to the wind range in town that I can use but it's snowing heavily right now. I had not forgotten that I was to print an example for you but have not had the right conditions yet.

Take my advice, I'm not using it anyway.

 
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Yrrah
(Login Yrrah)
YFOT

I read and understand you Don and appreciate that

January 31 2007, 6:54 PM 

you care sufficiently for objectivity to wait out the appropriate conditions.
I perhaps could choose an appropriate area of our property to set up a range that could be shot in reverse direction "out and back" in a steady wind.
We will be quite busy the next month or so and then we are off on another camping trip for some months and out of general circulation. I shall return to this when time and opportunity permit ....... Kind regards, Harry.

 
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Yrrah
(Login Yrrah)
YFOT

Here is Don's diagram together with one of my targets. As you can see

February 1 2007, 1:41 AM 

Here is Don's diagram together with one of my targets. As you can see my target does not fit any scenario in Don's diagram which has no points for impact in the two quadrants in which my pellets have impacted ( top right and bottom left quadrants ):





Yes the same 100 yard zero sight setting was used for all shots, only the wind direction and strength changed......... Kind regards, Harry.

 
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David Enoch
(Login DavidEnoch)
YFOT

Harry, does your rifle have a right hand twist?

January 31 2007, 4:45 PM 

Since your results were just opposite of the chart from Don I wondered if your rifle had left hand twist?

David Enoch


 
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Yrrah
(Login Yrrah)
YFOT

Right twist David ..... nt....... Harry.

January 31 2007, 4:56 PM 

nt

 
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(Login pneuguy)

Don, is it really your experience that the 30 degree...

January 31 2007, 7:49 PM 

...shift in wind bearing from #s 12 to 1, causes the radical jump in POI indicated in your diagram, making the #8 POI closer to the #12 than the #1 is?

Steve

 
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(Login DonMatzeder)
YFOT

Yep....

January 31 2007, 10:17 PM 

When the air make side contact with the spinning projectile, it makes a major move. I have noted several times that you feel the side to side movement is most noticable. I have found just the opposite. That movement is often masked by us, as shooters, believing that we have a trajectory problem and correcting our elevation with scope clicks but excepting lateral movement as the wind. Because of the peril of shooting a 12 oclock or 6 oclock wind, it is avoided by most all shooters. A change or "switch" of 1 degree can make a huge difference on POI from those wind directions. The shift of 5 to 10 degrees from 5 or 7 oclock makes very little difference.

Take my advice, I'm not using it anyway.

 
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(Login pneuguy)

Well, for what it's worth, Don, I can think of no physical/ballistic mechanism..

January 31 2007, 10:53 PM 

...that would produce such an effect.

The bullet/pellet emerges from the muzzle into a tremendous (100s or 1000s of mph) 12 o'clock relative wind produced by its own forward motion.

A few extra or fewer mph of additional airspeed contributed by an external headwind or tailwind is going to be inconsequential.

Steve

 
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(Login DonMatzeder)
YFOT

You're missing the point

January 31 2007, 11:45 PM 

The rotation of the pellet causes the pellet to "climb" or "dive" depending on which side the air is in contact with the side of the pellet.

Take my advice, I'm not using it anyway.

 
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(Login pneuguy)

Don, to begin with, your diagram shows the largest POI shift resulting...

February 1 2007, 12:02 AM 

...from a dead-on tail or head wind, with no side-on component whatsoever. Doesn't it?

Steve

 
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(Login DonMatzeder)
YFOT

Look close

February 1 2007, 7:11 AM 

and you will see those poi's slightly offset indicating a little push one way or the other. I assume the auther felt that it was near imposible to have a perfect tail wind. The pratical results match the diagram from my experience. I put 20,000 rounds down range this year. All at 50yds and all at paper with recorded results. I don't presume to understand the why of external balistics but I've gotten pretty good at predicting the results.

Take my advice, I'm not using it anyway.

 
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David Enoch
(Login DavidEnoch)
YFOT

Is your house behind you when you are shooting?

January 31 2007, 10:34 AM 

I was thinking you may have vetical swirling winds from the winds that come over the house or trees that affect the pellets when the wind is behind you.  I shoot parallel to my house sometimes and the wind coming over the house does different things at different speeds.  A low wind pushes the pellet down and away from the house.  A stronger wind just raises my impact point, and a strong gust pulls the pellet up and towards the house.

David Enoch



    
This message has been edited by DavidEnoch on Jan 31, 2007 10:38 AM


 
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(Login gks3)
YFOT

Yes...

January 31 2007, 11:14 AM 

My house is directly behind me:



The house is approximately 200yds from the sea (actually Hood canal but winds are mostly from the Juan de fuca strait).




And the winds do come up and over the house most of the time.
The wind flags do help show the wind but man, must be the time of the year because the wind is crazy lately. I'll watch the wind flags go from left to right and back again every 1-2 secs, seriously. The one closest to me (10yds) waves at me while the one furthest (40yds) is pretty steady usually blowing away and right from me. I know to take the closest one with most consideration and weight. This "snaking wind" is ridiculous though.

Thanks for your thought and input. Greatly appreciated.


greg in WA

 
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gino
(Login heightaddict)
YF

i also experience the same thing....may i ask

February 1 2007, 4:36 AM 

what range do you usually shoot? thanks

 
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David Enoch
(Login DavidEnoch)
YFOT

I was shooting at 30 yards

February 1 2007, 8:19 AM 

I was shooting at 30 yards.  The most I can get is about 35 yards in my yard.

David Enoch


 
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chevell
(Login chevell1322)
YF

factual

January 31 2007, 11:18 AM 

the charts on airgun ballistic programs aren't factual either,they will get you close in some cases but it won't be exact. The only fact is that the wind changes as the pellet goes through the air because wind isn't a constant,so predicting or adjusting the poi when it's windy will never be easy or exact.

 
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(Login ekmeister)
YFOT

I Hear That

January 31 2007, 11:47 AM 

A steady wind beats gusting wind any day.

Regards,

Ed

The Airgun Tune-Meister
http://members.aol.com/_ht_a/ekreally/myhomepage/business.html


"We can rebuild the squirrel. Make him stronger, faster...We have the technology"---S.M.

 
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gino
(Login heightaddict)
YF

shooting on a windy day

February 2 2007, 12:57 AM 






http://s107.photobucket.com/albums/m312/heightaddict/feb1/?action=view¤t=42yds.flv


SHOOTING WITH WIND LIKE THAT IS SO CHALLENGING.....GOT ONLY 3 OUT OF 5.

 
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Ed Krzynowek
(Login ekmeister)
YFOT

nt

January 31 2007, 11:46 AM 

nt


    
This message has been edited by ekmeister on Jan 31, 2007 11:49 AM


 
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