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Altitude vs. Barometric pressure

 
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  #92  
Old 11-24-2013, 10:27 PM
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Re: Altitude vs. Barometric pressure

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Originally Posted by RTK View Post
The kestrel will give you absolute or station pressure.
????? Mine will show Barometric pressure unless I set the reference altitude to 0.
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  #93  
Old 11-25-2013, 12:21 AM
RTK RTK is offline
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Re: Altitude vs. Barometric pressure

Correct, some are different than others, but if I set my altitude to 0 then it reads station pressure/absolute pressure.
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  #94  
Old 07-16-2014, 11:38 PM
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Re: Altitude vs. Barometric pressure (OR...)

OR... you can buy a Horus/Kestrel 4500 with the newer Applied Ballistics program and let it figure all this out for you, including such other niceities as coriolis effect, wind drift, etc. That device plus an accurate laser rangefinder will give you a very accurate firing solution.

"Altitude density" is the actual term for this barometric pressure conundrum. And that, of course is affected greatly by temperature and humidity.
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  #95  
Old 11-13-2014, 08:51 PM
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Re: Altitude vs. Barometric pressure

Hi I would like to chime in here. First let me introduce myself. I work for Applied Ballistics as Support Staff, so if you have any technical questions, or problems your emails come to me, and please feel free to email me with any questions you have at doc.beech@appliedballisticsllc.com

Now to help out some here. Density altitude is what is most important. That is the altitude the bullet feels, basically how the atmosphere feels to the bullet. But this is not the only thing that is going to affect your round. The direction you fire the round (east vs west) will affect the rounds vertical trajectory, this is relative to where you are latitude wise. East is High, West is Low. This has maximum effect at the equator and dies off at the poles. Shooting north or south is also the zero point for this effect. The other thing is closer you move towards the poles the more your round is is effected horizontally. This is basically effected by your latitude but has no effect based on direction of fire. If you fire north or east or whichever this stays the same, its based on your latitude. Then you have gyroscopic drift. Which is another story all together. As well as horizontal and vertical effects from the wind. So when you put all of this together, your weapons characteristics, your location, your atmospheric conditions, as well as other information you get what the Kestrel 4500 AB does for you. Its based on 3DOF + extensions. Basically it takes all of this information together, and gives you a firing solution in a matter of milliseconds.

I see some questions about the Kestrel have popped up. So the different Kestrels will give you loads of different information. In order to break it all down you would need a chart Compare Products | Nielsen-Kellerman but in short the only ones that will give you density altitude are the 4000 series and up. Secondly I saw some people talking about needing wifi in order to gather information. Their are options for this as well.

AB Tactical (Restricted to Military) is an off the grid program capable of giving you all the information you need. I plan to post about it on this forum in the future. The other AB Programs are capable of reading the instruments or GPS on a phone to give you information as well. But AB Tactical was designed to work off the gird from the ground up. No wifi needed, ever. All the factors that were discussed before are taken in to effect. Another thing to know is the Litz Curves. These are developed in a highly precise full time lab we have, and only available on AB software including the AB Kestrel. Others will say they use the Litz BC, but only AB uses the actualy Litz Curve (G1 or G7 as well if you choose).

Your best solution is of course to get a Bluetooth model. This will input the information for you in to the applications. Battery life is a non issue with a Kestrel, they have outstanding battery life. With a Kestrel that has Density Altitude you no longer need your gps location, or your elevation. It will tell you what the round "Feels" as it travels through the air.

If you have any questions or would like me to answer anything in detail please feel free to ask, or if you would like you can privately email me.
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  #96  
Old 11-14-2014, 05:38 PM
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Re: Altitude vs. Barometric pressure

DocUSMCRetired I know it's long but you should read previous posts in this thread.
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  #97  
Old 11-14-2014, 05:59 PM
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Re: Altitude vs. Barometric pressure

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Originally Posted by Mikecr View Post
DocUSMCRetired I know it's long but you should read previous posts in this thread.
Thank you, and I will certainly take the time to do so. This was just in response to some posts I have seen in this section. I will go back though and try to answer other questions here. For that last post I tried to cover some questions that have been asked over the last couple months.
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  #98  
Old 11-14-2014, 09:28 PM
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Re: Altitude vs. Barometric pressure

Thanks Doc,
Your input was needed here, especially regarding the Kestrel 4500/AB model. Unless it is a military device there is no other device I know of that will sense and calculate for so many environmental parameters as that unit for rifle firing solutions. It even considers internal ballistics in the form of twist rate that must be entered into the K 4500/AB to calculate spin drift.

Also the fact that Kestrel has now added Applied Ballistics software gives me even more confidence in it. Brian Litz and company have actually tested the ballistics and not just extrapolated from ballistic theory. As the song says, "There's nothin' like the real thing Baby."

My understanding of altitude density is that is the TRUE factor that matters, not actual altitude,d because, as you mentioned above, it is the atmospheric "density" the bullet must pass through. A very hot day (say, 100 F.) at 6,000 ft. and a very cold day (say 0 F.) at the same altitude, given the same humidity, will produce very different atmospheric densities. Hot air is "thin" (less atmosphere) and cold air is dense. Of course relative humidity and air pressure differences caused by weather fronts is a variable the also unit takes into account.


The K 4500/AB unit's internal compass is used to calculate north/south coriolis effect and east/west effect (I forgot the term for this).

Now if there were a way to use laser light to calculate average wind over the distance-to-target we'd have an even better solution. As it is the wind at the shooter's position is the most important reading in terms of effects on bullet wind drift and by taking two readings, the full wind and the wind on the line of firing to target the unit calculates a proper wind value.

QUESTION: With all other factors being equal will, for example, a .30 cal., 200 gr. bullet fired from a .300 Win mag cartridge with a 1:10 twist barrel drift more than the same bullet fired from a 1:8 twist barrel? I'd guess the faster twist rate gives more gyroscopic stability and perhaps less spin drift.
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