Range Report JBM Ballistics?

[scout1]

I have a question concerning data input on the JBM site.
In their section for trajectory cards they ask to input the altitude. I'm assuming they are asking for the density altitude, but they don't really say. Anyone know for sure? Are they asking for the density altitude or just regular altitude?

Thanks.

 

[BryanLitz]

Re: JBM Ballistics?

It's just altitude.
-Bryan

 

[Lindy]

Re: JBM Ballistics?

It depends upon which section of JBM you're in. If you using this page:

http://www.jbmballistics.com/~jbm/cgi-bin/jbmtraj-5.0.cgi

You may be entering altitude and temperature, and telling the program to compute standard atmospheric values, or you may be entering station pressure from a Kestrel or other source, in which case you should leave the altitude set to zero. If you don't understand that, see:

Barometric Pressure and Ballistic Software

If you're using this page:

http://www.jbmballistics.com/~jbm/cgi-bin/jbmcard-5.0.cgi

You are entering the atmospheric parameters in the form of density altitude numbers.

 

[Falar]

Re: JBM Ballistics?

Is it just me or is something wrong with the calculators there? Whenever I select a bullet and fill out all of the lines it won't let me calculate until I enter values for the bullet, even though I shouldn't have to because I'm selecting ones from the database.

 

[scout1]

Re: JBM Ballistics?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">It depends upon which section of JBM you're in. If you using this page:

http://www.jbmballistics.com/~jbm/cgi-bin/jbmtraj-5.0.cgi

You may be entering altitude and temperature, and telling the program to compute standard atmospheric values, or you may be entering station pressure from a Kestrel or other source, in which case you should leave the altitude set to zero. If you don't understand that, see:

Barometric Pressure and Ballistic Software

If you're using this page:

http://www.jbmballistics.com/~jbm/cgi-bin/jbmcard-5.0.cgi

You are entering the atmospheric parameters in the form of density altitude numbers.
</div></div>

Thanks Lindy. Thats the way I had interpeted it, and had applied that to the way I had used JBM. Just wanted a second opinion.

 

[memilanuk]

Re: JBM Ballistics?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Falar</div><div class="ubbcode-body">Is it just me or is something wrong with the calculators there? Whenever I select a bullet and fill out all of the lines it won't let me calculate until I enter values for the bullet, even though I shouldn't have to because I'm selecting ones from the database.</div></div>

Must be just you.

Never had that problem (and yes, I just went there and tried just to be sure). Maybe your bullet selection step didn't work right somehow? I've found the person behind the site @ JBM to be pretty responsive to questions if you even *think* you have a problem - the obvious caveat being 'ask politely'

 

[Pierce33]

Re: JBM Ballistics?

ok, i am a little confused on if i want the "Std. Atmosphere at Altitude" checkbox checked or not. If i am entering the actual altitude and barometric pressure(not station pressure) should it be?

 

[Lindy]

Re: JBM Ballistics?

If you are entering the BP and altitide, that box should be checked.

 

[Pierce33]

Re: JBM Ballistics?

ok, i have been reading over your articles, now if im not using the DA method and just entering the standard BP and the rest of the information, is that a good way to do it?

Also if i continue to enter it this way, should i be entering in all of the information? ie. humidity and temp, always right?

Sorry if these are dumb questions, im just trying to figure this all out

 

[Lindy]

Re: JBM Ballistics?

Those are not dumb questions.

Putting in the sea-level-referenced barometric pressure and the altitude is not <span style="font-style: italic">quite</span> as accurate as putting in the station pressure. But if you don't have a Kestrel or other source of station pressure, it's the best you can do, and mostly it's good enough.

You should always put in the temperature. If you don't have a source for humidity, you can just put in 50 percent, and you won't be far off.

 

[Mag 300]

Re: JBM Ballistics?

you could call the local airport service to get barometric pressure but ensure your at the same altitude. otherwise the kestral is the only way
Bill

 

[Lindy]

Re: JBM Ballistics?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">otherwise the kestral is the only way</div></div>

Well, not quite. There are quite a few watches which have atmospheric pressure sensors. I have a Casio Triple-Sensor Pathfinder which serves that purpose very well. It also has a digital compass and other features.

 

[Pierce33]

Re: JBM Ballistics?

yup i wear a suunto vector that has altitude, BP, temp, compass, and even the time!

 

[hifly78]

Applied to Ballistic FTE Software

Hi Lindy,

Thanks, I read your article on Pressure and Ballistic software.

Still a little confused about the Ballistic FTE software.

When I enable the Atmosphere for the current atmosphere page I get a little confused. It makes sense that altitude and barometric pressure (corrected to sea level) is what I should enter along with the temp and humidity for current location.

If that is right then when I enable standard pressure (as 29.92)it then corrects the pressure for altitude. So if I want to be more accurate should I be putting in ambient pressure not barometic pressure with the altitude at zero.

I've tried to run parallel calcs using pressure and temp for standard atmosphere then entering ambient pressure with the altitude at zero and just not jiving.

If you are familiar with this any thoughts on what is right.

I also have the knight bullet flight and it seems that Barometic Pressue not ambient pressure is what I should enter.

 

[Lindy]

Re: Applied to Ballistic FTE Software

I don't have that software, so I can't answer questions about it.

You might try entering the same parameters into JBM Ballistics to see how it compares.

 

[ReaperDriver]

Re: Applied to Ballistic FTE Software

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hifly78</div><div class="ubbcode-body">Hi Lindy,

Thanks, I read your article on Pressure and Ballistic software.

Still a little confused about the Ballistic FTE software.

When I enable the Atmosphere for the current atmosphere page I get a little confused. It makes sense that altitude and barometric pressure (corrected to sea level) is what I should enter along with the temp and humidity for current location.

If that is right then when I enable standard pressure (as 29.92)it then corrects the pressure for altitude. So if I want to be more accurate should I be putting in ambient pressure not barometic pressure with the altitude at zero.

I've tried to run parallel calcs using pressure and temp for standard atmosphere then entering ambient pressure with the altitude at zero and just not jiving.

If you are familiar with this any thoughts on what is right.

I also have the knight bullet flight and it seems that Barometic Pressue not ambient pressure is what I should enter.
</div></div>

Yeah, the baro pressure function on the Ballistic FTE (iphone) is the most confusing to me. I'm very famailiar with using baro pressure in my job (pilot) but the baro pressures that the iphone loads when getting auto data makes no sense. For instance, when the REAL nearby airport altimeter setting might be 29.90, the baro pressure that the iphone reports is usually something like 26.55. I'm within a 1000 ft elevation or less of the airport but an altimeter setting that low is making zero sense.

Do ballistic calculators use something different for pressure than what I understand as "altimeter setting"?