# Humidity effects on External Ballistics.

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by 7mm Eclipse, Jul 25, 2012.

1. ### 7mm EclipseWell-Known Member

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Jan 19, 2009
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.

2. ### SackettWell-Known Member

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Jul 6, 2011
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....

3. ### Joe KingWell-Known Member

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Apr 29, 2012
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

4. ### MikecrWell-Known Member

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Aug 10, 2003
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
Insignificant(.003)

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.