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Humidity the multiplier

 
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  #1  
Old 01-04-2010, 10:18 AM
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Join Date: Nov 2008
Location: Central Pennsylvania
Posts: 4,022
Humidity the multiplier

So this humidity thing was bugging me. I decided to run the numbers through JBM to see if my theory held weight and whether or not that I have in fact read an article discussing this very issue. So all things being equal; Baro, temp, altitude, I just changed the humidity to see what effect it changed on velocity and flight. Here is what I came up with:


Rifle is an assumed load because I was crunching numbers for another thread:
338 Norma 2750fps 300grnSMK

First the numbers
75 degrees temp, 100%Humidity, 1000' elevation, Baro 28.82 (close enough)
39.55 MOA 1506fps 1510 ft. lbs 1340yrds

Same as above except the Humidity is changed to 30%
39.04MOA 1505fps 1508 ft. lbs. 1330yrds.

So as you can see, all things being equal which can happen in PA except the humidity, a more humid environment allows for better ballistics. Can somebody explain this? Now granted it is not very much and I'm sure only really noticeable at extreme range, but it is still a factor. Hopefully Bryan Litz is paying attention.

Tank
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  #2  
Old 01-04-2010, 10:53 AM
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Re: Humidity the multiplier

The higher the humidity, the less dense the air, the more efficient the bullet will move though the air.

Contrary to what our senses tell us (high humidity make the air feel heavier or thicker) high humidity air is less dense air than dry air (low relative humidity air). Bullets will cut through less dense air more efficiently.

As you confirmed, humidity plays a relatively minor role compared to temperature and atmospheric pressure. It can just about be ignored, but if you know the humidity and you're shooting very long range, and your ballistics software can correct for it, then I do enter it as part of environmental conditions for predicted drops.
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  #3  
Old 01-04-2010, 11:40 AM
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Re: Humidity the multiplier

It can't be explained any better than what phorwath said.
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  #4  
Old 01-04-2010, 11:44 AM
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Re: Humidity the multiplier

I thought I was right in another thread, but wanted to make sure. I would hate to give bad info.

Tank
__________________
Matthew 7:13-14
"Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. [14] But small is the gate and narrow the road that leads to life, and only a few find it.

If you find your self in a fair fight, your tactics suck!- Marine 1st Sergeant Jim Ryfinger

Friends don't let friends develop canonitis!-chucknbach

arguing over the internet is like the special Olympics....even if you win, you are still...special!
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  #5  
Old 01-04-2010, 03:15 PM
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Join Date: Jul 2007
Location: Arkansas (Home of Record)
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Re: Humidity the multiplier

Quote:
Originally Posted by bsl135 View Post
It can't be explained any better than what phorwath said.

+1, I usually listen when these guys speak...or type...
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  #6  
Old 01-04-2010, 03:44 PM
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Join Date: Nov 2008
Location: Central Pennsylvania
Posts: 4,022
Re: Humidity the multiplier

Thanks guys, I appreciate the replies.

Tank
__________________
Matthew 7:13-14
"Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. [14] But small is the gate and narrow the road that leads to life, and only a few find it.

If you find your self in a fair fight, your tactics suck!- Marine 1st Sergeant Jim Ryfinger

Friends don't let friends develop canonitis!-chucknbach

arguing over the internet is like the special Olympics....even if you win, you are still...special!
Reply With Quote
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