Altitude vs. Barometric pressure

Bart B

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Dec 25, 2005
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I've watched folks shoot their 308 Win match rifles at Camp Perry's 575 foot elevation in 1000 yard matches with the same ammo and zeros used at the NRA Whittington center's 6600 foot level put their first shot off the 6 foot square target's bottom. Then do it several more times before realizing the thicker air slowed their bullets down enough to do that.
 

Mram10us

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Oct 19, 2019
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Planes like low density altitude, bullets like high density altitude
 

Dog Rocket

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Mar 17, 2018
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Washington State
Dog Rocket, which Casio model do you have? I called Casio to inquire about a model that gives SP and the rep could not tell me a model. That would give me a backup to my Weathermate Weather Hawk.
I have a GDF-100. Several models of the ProTrek will do it also. The rep you talked to probably didn't have any idea what station pressure was. Any of the G-Shocks that have altitude sensors will show both altitude (effectively, pressure altitude), as well as the raw data of station pressure.

I've wanted a RISEMAN for quite sometime, but the reality is that this one does everything I need.
 

PApa Black

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May 23, 2012
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Example: RSI Ballistic calculator calculates that at sea level in 59 degree air and 29.53 BP a bullet with a .540 BC at 2700 FPS zeroed at 300 yards will drop 307.9" at 1000 yards.

The same program, same BP, bullet, velocity, zero, temprature, but change the altitude to 5000' and the bullet drop is calculated to be 315.8 with the same barometric pressure imput.

The differance is 7.9"

I always thought that the actual pressure and not altitude changed the bullets perfomance. I know pressure changes with higher/lower altitudes go hand in hand, but thought that altitude in and of itself had no effect on the bullet and just the pressure change with the altitude.

Any ideas?? Is the RSI program correct or is it a glitch?
I use this program: fill in all the blanks and the correct answer is calculated: https://www.jbmballistics.com/ballistics/calculators/calculators.shtml
 

Bart B

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Dec 25, 2005
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Planes like low density altitude thin air?

Bullets like high density altitude thick air?

Isn't that backwards?
 

Mikecr

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Aug 10, 2003
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NC, oceanfront
Mram did not suggest that low density altitude is thin air. It isn't.
YOUR confusion provides another example of why shooters need to steer clear of DA for solutions.
 

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