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Humidity effects on External Ballistics.

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Unread 07-25-2012, 11:20 AM
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Join Date: Jan 2009
Location: Atlanta, GA
Posts: 56
Humidity effects on External Ballistics.

What is the effect of high humidity, drizzle, light rain and snow on External Ballistics?

The ballistic calculators use a humidity variable in the calculations but I am curious about how small to large water droplets and snow effect the flight of the bullet during long range hunting.
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Unread 07-25-2012, 12:31 PM
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Join Date: Jul 2011
Location: Troy S.C.
Posts: 137
Re: Humidity effects on External Ballistics.

I asked this question a few days ago on the 7mmSTW Brotherhood thread...The responses that I received observed that under 1000 yds rain has little to do with it, plus if it raining or snowing that hard you would not be able to see the target anyway. I tested it the other day with 60% humdity and a light to steady rain at 500 yds and saw no noticable change in my 7mmSTW's POI....

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Unread 07-25-2012, 01:10 PM
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Join Date: Apr 2012
Location: The cold part of Montana
Posts: 1,391
Re: Humidity effects on External Ballistics.

Hi humidity + less air density, low humidity = higher air density. I ran it across a modified point mass cal and couldn't get a value change at 1600yrds, so apparently it doesn't have much effect beyond visibility

The ballistics calc Brian supplies with his book showed 1.66" at 1000yrds with the generic values, I ran it at )%humidity and 100% humidity changing only those 2 values
Keep in mind the animals we shoot for food and display are not bullet proof. Contrary to popular belief, they bleed and die just like they did a hundred years ago. Being competent with a given rifle is far more important than impressive ballistics and poor shootability. High velocity misses never put a steak in the freezer.

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Unread 07-26-2012, 06:27 PM
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Join Date: Aug 2003
Location: NC, oceanfront
Posts: 4,197
Re: Humidity effects on External Ballistics.

Relative humidity plays more of a role at higher temps.
For example:
105VLD ICAO G1 BC @ 3Kfps = ~.525
ICAO = 59degF, 0%RH
Change only to 90%RH local BC = ~.528

Now, change to 100degF, 0%RH local BC = ~.566
And 100deg, 90%RH local BC =~.579
A little more significant(.013)

At 1kyds drop changes from RH spread:
@.525, drop = 320.8
@.528, drop = 319.8
1" drop diff
(also 0.6" in 10mph drift)

@.566, drop = 307.5
@.579, drop = 303.8
3.7" drop diff
(also 2.1" in 10mph drift)

No predicting change to tune really.

Most consider these differences to be insignificant, as they have considered so with horizontal & vertical coriolis, gyroscopic drift, and magnus effect.
It's when you start adding all these together that single shot ACCURACY becomes more of an abstract.
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