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How Much Does Barometric Pressure Change?

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Unread 08-02-2008, 11:18 AM
Join Date: May 2001
Posts: 6,201
Shawn, I know! I remember a 690 muley I killed in MT. First shot kill but afterward I realized I had made two small errors in my ballistics setup. Luckily they offset each other and I got to eat the venison anyway.

By the way, I have always adjusted for elevation, just not other pressure changes.

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Last edited by Len Backus; 08-03-2008 at 07:14 AM.
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Unread 08-03-2008, 02:57 AM
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Join Date: Mar 2006
Posts: 180
The use of "Density Altitude" as a ballistic reference takes into account barometric changes, as well as air temperature and humidity (the least influential).

I use a Kestrel 4000 to give me direct readings, but it can be manually figured if desired.

Density altitude - Wikipedia, the free encyclopedia

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Unread 08-03-2008, 03:51 AM
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I'm no weather wizard but the way I understand it is if the Barometer drops so drastically that it effects your shooting, you are probably shooting it a thunderstorm. which most of us arnt shoot/hunting much in anyways. JMO.
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Unread 08-04-2008, 01:02 AM
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I set my Kestrel to read station pressure. I just returned from a scouting trip. The pressure at home before leaving was 25.49 (5889'). The pressure where we were scouting (11,000') was 20.??. Five inches or more pressure change from where i shoot to where I hunt!
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Unread 08-04-2008, 08:33 AM
Join Date: Jun 2007
Location: North Idaho
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That is the problem. Five inches less pressure will make you shoot quite a bit flatter even at closer distances.
Shawn Carlock
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Unread 08-04-2008, 07:20 PM
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Join Date: Jan 2005
Location: OK
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I have a problem with this, that may-be one of you can help me with?

I'm at roughly 1000 ft with WI muggy conditions. I just started loading for my 300Rum.

Berger 210 @ 2950fps, I will be hunting at 11,200-12,200 feet in four weeks, CO high country mulies. I'm printing a drop chart for home on JMB calculations.

I need to print a drop chart for altitude that is reasonably close, I will then shoot and adjust/confirm things when I reach the hunt area.

What or how should I enter the data to get the info close with the JMB basic balistic calculator?

Do I need to enable the "standard atmosphere at altitude?"

I assume I need to keep "corrected pressure" enabled?
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Unread 08-04-2008, 08:05 PM
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Join Date: Dec 2002
Location: mathias wv
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ok, dumb country hick here, don't know if I do it right or not but here's how I do it

I have a casio sea-pthfinder watch which after I press the button in 2 seconds it gives me station pressure (bar pressure where I'm standing) I enter this into exbal and enter zero for the altitude.
My understanding of it is higher altitude lowers the bar pressure, which raises the bullets BC.
this change in the BC is why altitude effects the bullets flight, so if you know your bar pressure, exbal compensates for it and altitude can be left at "0". if you put in a bar pressure reading and an altitude reading it over compensates, Is this correct?
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