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Extreme Long Range Hunting & Shooting (ELR) Over 1,000 Yds.


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Wind reading for +1K shots

 
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  #8  
Old 08-05-2012, 10:24 AM
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Re: Wind reading for +1K shots

I find the wind and learning how it moves through an area to be one of the things that I like about ELR shooting, it's something that the ballistics table won't tell you and your Kestrel may only give you hits of. I really like watching an area with a wind while snowing then during the spring shoot the area and evaluate what is influencing the wind path.

One key thing clicked for me this spring in my shooting area and that was paying attention to the prevailing wind direction, we're sending bullets 100+ ft over the line of sight to the target and it's getting into air flows that are determined more by the natural air flow in the area vs the air that is more affected by the terrain.

I've really had a hard time using trees as an indicator for wind, I think they are just to stiff in my area and if they are moving it's a wicked wind. I do use them a lot to listen for the wind velocity, you can really hear the wind coming up and down.
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  #9  
Old 08-05-2012, 12:15 PM
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Re: Wind reading for +1K shots

Yep, he needs to re-visit his statement on humidity, bet it was a typo.
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  #10  
Old 08-05-2012, 12:38 PM
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Re: Wind reading for +1K shots

Just playing with the Atrag, using inputs for a 175 SMK at 2650 there is only around one tenth of a mil difference in vertical drop at 1000 yds when comparing 10 percent vs 100 percent humidity. In the case of the 375 Cheytac it is barely measurable.

If shooting a Rd with low velocity or very low BC the effects are much more pronounced.
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  #11  
Old 08-05-2012, 09:05 PM
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Re: Wind reading for +1K shots

Boss Hoss,

I make no derogatory statements about Mr Speedy Gonzalez ability as a shooter or his record in competition. He is obviously a well known a and respected shooter. However his statement on the effect of humidity is in error. Simple as that.

This may be a typo or a misunderstanding of the facts, I don't know. He states that a 20% change in humidity will result in a 1 MOA change in point of impact. This is a vague statement as he does not define a distance that this 1 MOA change is made.

In no way will a 20% change in humidity result in a 1 MOA change in POI at 100 yards or any distance under 1000 yards. In actual fact, the only change that I can find at 1000 yards is a mere 0.1 MOA. and that is in the opposite direction to what he states it will be.


The effect of atmospheric conditions on a bullets trajectory is due to changes in air pressure, temperature and humidity. Variations in these three things, result in a change in air density and the speed of sound.

While changes to air density have a large effect bullet drop, changes in the speed of sound have only a very minor effect on trajectory and mainly at extreme long range where the transonic barrier is encountered.

A change of humidity from 0% to 100% at 59 degrees F, has only a 0.2% change in the speed of sound. So only a minor effect at best.

Please read the effect on air density due to changes in humidity below and in the link provided, it helps describe why the effect on trajectory is opposite to what Mr Speedy states.

The effect on air density can be read here..... Density of air - Wikipedia, the free encyclopedia
But in short........ The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear counter-intuitive.
This occurs because the molecular mass of water (18 g/mol) is less than the molecular mass of dry air (around 29 g/mol). For any gas, at a given temperature and pressure, the number of molecules present is constant for a particular volume (see Avogadro's Law). So when water molecules (vapor) are added to a given volume of air, the dry air molecules must decrease by the same number, to keep the pressure or temperature from increasing. Hence the mass per unit volume of the gas (its density) decreases.

A lot of the other tips that Mr Speedy gives sound like good advice.

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  #12  
Old 08-06-2012, 12:12 AM
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Re: Wind reading for +1K shots

So if the elk I'm going to eat is standing by a range flag and that range flag is drooping a little more than the wind conditions appear to be and I'm a little more damp I should expect the bullet to be just a smiggen faster when it reaches my meal and therefore may not need to raise up on his chest as much (distance dependent). I believe Linda Miller mentions this in "The wind book for rifle shooters". The most "common" thing to think is the humidity will make the air "thicker". In reality it makes the air "thinner" (for reasons you just explained).

Is that fair to say? or am I wrong?

Last edited by drbill; 08-06-2012 at 12:13 AM. Reason: add
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  #13  
Old 08-06-2012, 09:23 PM
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Re: Wind reading for +1K shots

Is that fair to say? Or am I wrong? ? ? ?
I don't think there is a right or wrong in shooting but more of an effective and not quite so effective approach. The statements made on humidity are also published in FM 23-10 HQ Dept of the Army 17 August 1994. But this thread isn't on humidity, so here's what I do for reading the wind:
1. Set up wind flags at the bench, half way to the target, and at the target. I use these
http://www.brflags.com/
Extra large with HIVIS colors, obviously they don't go up hunting (not because that is ridiculous but because if don't camp where I plan to shoot from they will probably be stolen).
2. Get a wind reading from the Kestral (I use the line it up to point of aim method and use the reading as a full right or left value).
3. Observe nature from the muzzle to the target and decide if I need to make an additional correction (so far I have only corrected for wind at the and apply this correction.
4. Observe the wind flags I've set up because nature and the wind flags tell 2 very different stories (the flags are super sensitive).
5. Get all dialed in and ready to pull the trigger.
6. Start all over again because the condition has changed.
7. Wait for the same condition because this wind reading is kicking my ***** right now.
8. Record my hit or miss and try to understand why I hit or missed.
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  #14  
Old 08-07-2012, 12:40 PM
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Re: Wind reading for +1K shots

My comment was an attempt at humor and the "confirmation" of my understanding of humidity. I use Source for Super-Sized NRA Range Flags Daily Bulletin from the Starr family atop 1.5 or 2 - 1 3/8" chain link top fence eye hooked t-posted in ground. $50 total or less when done. The difference in long range and ELR hunting has many factors that each of you have described and I am greatly thankful for your comments. Some individuals do not have/make a chance (but should for reasons explained) to visit their favorite hunting grounds in the off season to practice on "their" terrain. Snow at elevation, heck sometimes you have 80 degree days and no snow and maybe next year feet of snow. I can "see" each individuals "understanding" on this topic and its a good topic at that. I can see how practice at these locations will build the confidence of a shooter and of course keep ethics in check. As each year passes one would understand his hunting ground more and more and the increased ability for ELR in that area. Thank you.
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