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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/22/2009 at 12:41
Graysteel View Drop Down
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Hey folks,

What do you people prefer for external ballistics software? I have used NightForce in the past but I found there to be a few bugs and when I went to update it I found perry-systems (the authors) to be rather unfriendly.

I have been considering getting Sierra or another brand anyone have any suggestions?


Edited by Graysteel - August/24/2009 at 10:39
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/22/2009 at 14:25
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exbal works pretty good, and the nf package is a repackage of that . Patagonia makes one that uses a curve fitting process instead of numerical integration. what are doing that jbm free on the net can't do?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/24/2009 at 10:44
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I finally got them to send me my upgrade for exbal/Nightforce. I had paid for it they just needed to update their records. It seems their customer service works better if you order directly from perry-systems.

I wasn't doing anything specific, just wondered what folks liked.  For instance, I hadn't messed with http://www.jbmballistics.com/ until you just mentioned it.

I just learned about a cool resource :) Thanks!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 04:39
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The only disadvantage to JBM is that you have to have internet access to use it. Otherwise, it has always worked well for me, especially after I switched to the G7 BC model for VLD bullets. (Recently, JBM added a bunch of known G7 BCs provided by Bryan Litz of Berger bullets). Using the right BC model minimizes the deviation across different velocities. I also use Ballistic on my iPod Touch. It has the advantage of being easily portable in the field. However, I have yet to get it to match JBM's output past 400 yards. (I need to consult the author again to figure out the descrepancies).

Anyway, if you establish velocities well it works to use JBM to generate a drop chart you can print out and verify in the field. Typically, I look at my 150 and 300 yard POIs because I'm interested in an 8" kill zone for big game that plots out to 4" high @ 150 and 4" low @ 300 with a zero around 260 yards. But I'll also dial in shots out to 600 (which is all I care about with a .308). At the end of my current load testing, I'll tape a small drop chart to my stock because I'm not going to worry about battery life.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 05:43
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Update to my previous post. After some fiddling with Ballistic's settings - mostly with its atmospheric corrections - I've been able to get it to match JBM almost to a T...and certainly well within the range of actual ability, i.e. @ 1000 yards the discrepancy between drops is .64" and .31" for windage. I will post more on what the settings should be since it wasn't clear from the Ballistics site or the emails I exchanged with its author. Just wanted to correct what could be considered a negative post about Ballistic. It can be as accurate as JBM if set properly.

Edited by jonoMT - August/27/2009 at 05:43
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 06:30
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How do you know which one is "truth"?...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 08:51
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good question, but the problem usually comes from the inputs, rather than the output. Patagonia can be used to calculate the percentage difference based on a comparison between the closed form expression for the curve and one given by the data points. jbm and sierra can be "judged" by knowing how many steps they used in their integrater.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 09:14
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Do for say Huh?  Whacko
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 09:27
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Originally posted by Kickboxer Kickboxer wrote:

How do you know which one is "truth"?...


The answer is: Neither. The only true way to know is by field testing, which I expect you already well know. What I was trying to do was to get Ballistic's settings "correct" so that its results would be the same as JBM, since both use basically the same algorithms. So it wasn't an issue of trying to "make the terrain fit the map" or getting the data to fit my expectations. It's just that Ballistic has a different approach to handling a default atmospheric setting and a "current" setting (which apparently if you have an iPhone instead of a Touch like I do and actually shoot within range of a cell tower it can download from NOAA). I had to turn off the default atmosphere and then manually enter the same values I use in JBM into the Current atmosphere AND turn off "Standardize Pressure" so I could enter 29.92, then the output matches far closer than one can practically shoot.

From there it's all about field verification. At least now I can try a different load chronographed at some other velocity and dial in some come-ups. (BTW, the 29.92 Hg barometric pressure is just about the long-term average for Montana, according to the NWS office in Great Falls. I suspect that's probably true of most places).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 09:57
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 (BTW, the 29.92 Hg barometric pressure is just about the long-term average for Montana, according to the NWS office in Great Falls. I suspect that's probably true of most places).
[/QUOTE]
 
JonoMT, the 29.92 that the NWS is quoting is corrected for altitude. The actual or raw value will be about 3.5 inches Hg lower. The NWS corrects for altitude so it is easier to see hi and low pressure ridges across the map. If they only showed the real values as read it would look like Denver was always in a low pressure ridge and places at sea level were in High pressure ridges.
The airport in GF shows to be at 3678 ft. So if the actual pressure was 26.29 it corrects to 29.92.
Some of the software wants the as read value while others take a standard such as 29.92 and adds an altitude correction to lower the calculated number.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 13:48
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GLZ, that difference between corrected and uncorrected values confused the heck out of me at first. To clarify two things:

1) I'm using the corrected value and different software handles that in a variety of ways. At least I finally figured out what settings to turn on or off in Ballistic to get it to calculate by JBM's standards.

2) The figures I got from the NWS office in Great Falls were not for there (or as I mis-remembered for the entire state). They were as follows:

"For Helena, for the period 1971-2000:

 

Mean Station Pressure: 26.02 inches of Hg Mean Sea-Level Pressure: 30.06 in of Hg"


That still makes me think that using a corrected pressure at or near 29.92 will not result in much error. In fact, a quick change resulted in an additional drop of just 1.15 inches @ 1000 yards. Since those figures were almost certainly derived at the Helena Regional Airport, which is at 3800 feet, I'd want to use the uncorrected value of 23.979 for 6000', which is where I do most of my load testing and hunting. Of course as soon as I change the settings in Ballistic to do that it no longer agrees with JBM. Guess it's back to the drawing board! I'm going to assume that JBM is correct regardless of whether I use the corrected pressure or uncorrected with the "Pressure is Corrected" checkbox unchecked because either gives the same results.


Edited by jonoMT - August/27/2009 at 13:50
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 14:18
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29.92 is the standard for "standard air". The only time you will run into a problem is when you have a front move thru and the pressure drops/raises or your inputed altitude is off substantialy. If you use GPS for altitude it should not be a problem. If you use a barometric style altimeter your elevation can be way off due to fronts.

It all boils down to how the software calculates density altitude.
Looks like you got JBM figured out.
My point was you have to give the software what it wants to get good results. GIGO.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 14:43
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Originally posted by Dale Clifford Dale Clifford wrote:

good question, but the problem usually comes from the inputs, rather than the output. Patagonia can be used to calculate the percentage difference based on a comparison between the closed form expression for the curve and one given by the data points. jbm and sierra can be "judged" by knowing how many steps they used in their integrater.
Do you know that??
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2009 at 15:49
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Do I know what?? sierra and jbm use a Runge-Kutta, on the differential equations  which are a usually between 4-5 coupled linear differetial equations and patagonia uses a form fit method. (sum of least squares more than likely). Given correct value of inputs for either the two methods will list a series of ouputs the difference between the closed form of the equation and the output being the error. Basic Numerical Analysis.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/28/2009 at 22:42
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Here's what I did to get Ballistic much closer to JBM...at least so that a trajectory for my .308 is very close out to 1100 yards. You have to turn off the Zero Atmosphere, then set the Current Atmosphere so that temp, humidity, and altitude are the same as JBM. Provided you are using 29.92 as the value in JBM and have checked "Pressure is Corrected", you then set "Standardize Pressure" off in Ballistic and use 29.92 as the Barometric Pressure. Seems totally bass ackwards, but it does match that way.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/29/2009 at 07:48
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Originally posted by Dale Clifford Dale Clifford wrote:

Do I know what?? sierra and jbm use a Runge-Kutta, on the differential equations  which are a usually between 4-5 coupled linear differetial equations and patagonia uses a form fit method. (sum of least squares more than likely). Given correct value of inputs for either the two methods will list a series of ouputs the difference between the closed form of the equation and the output being the error. Basic Numerical Analysis.
You are making some assumptions you can't be sure are vaild.  I just asked if you KNOW they are using the same method.  There is a whole litany of Runge-Kutta methods, and depending on the order chosen can yield a slightly different result.  Do you know if they are using Fehlberg or similar?  I have not researched it, and do not know what methods the indicated ballistics solution programs are using.  You seemed to have some firsthand knowledge...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/29/2009 at 08:58
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talked with both sierra and the people at patagonia, about their math. have used runge-kutta-fehlberg methods to find computed solutions and estimation of the truncation error in Matlab to help decide when to adjust the step size. Sierra was using 4th order Runge-kutta at the time I talked with them. From the NAG library there is only a finite  number of methods they can use. Its easy to narrow it down. My interest was for fun not to "check" them out. Each method can give slightly different results as jonoMt has pointed out in his post and using simulation techniques can jiggle them to come out the same. I use the methods daily except the areas of interest are 2nd order non-linear quasi-periodic biological systems.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/29/2009 at 11:40
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Roger, Dale... was not questioning you at all.  Just OBTW, we use Matlab in some simulations and have had make similar decisions.  Great tool, overall, though... very fast model development. 
 Most of the ballistics calculation programs use modified methods and produce similar but slightly to very different results.  I just tried out two ballistics programs for the Mac, both were POS.  I can't even fathom what method they MIGHT be using.  No relation to a real trajectory.  
This should interest you:

First complete picture of a molecule...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/31/2009 at 12:09
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Wow. I can't begin to pretend to understand what all that math is about. But I can say that what matters most for the lay person here is that good input data will produce good results (i.e. avoiding GIGO). I started with JBM and also consulted with its author to make sure I'm doing the right things. Then I got Ballistic (which doesn't run on a Mac...or PC...but does run on the iPhone or Touch) to basically output the same results.

A couple of things I learned or confirmed:

You want to get your data input as accurate as possible but once that's done, there isn't a lot of difference in drops out to mid-range distances, e.g. a .308 firing a 165gr. @ 2650 fps out to 600 yards. So, for example, if I compare the following the difference will be 3.8" @ 600 yards and only .4" @ 300 yards:

a) 80F, bar: 30.50, humidity: 25%; altitude 4500 (warm, clear, sunny, extra high pressure day!)
b) 20F, bar: 29.50, humidity: 75%; altitude 9000 (cold, snowy day twice as high)

Granted, moving to a higher altitude is offset by lowering the temperature and pressure. Try just changing one variable for a truer scientific analysis. (But I can't help but compare different conditions in their totality sometimes). Getting back to the data input, if you are using a boat-tail or VLD bullet, be sure to use the G7 drag model. If possible, get the Litz data for your bullet. JBM has all these now, although it does not output the BC for them. If you want that, do like I did and buy Litz's excellent book on ballistics. (Perhaps by the time I'm done reading it I'll understand a tenth of what Dale and Kickboxer do).

Get your temperature, altitude, barometric pressure, humidity as close as you can. In JBM, if using a corrected barometric pressure, such as one derived from a weather map, make sure the "Pressure is Corrected" box is checked and that you've entered the altitude. It's also important that you measure the sight height correctly (distance from center of barrel to center of reticle) and that you know the velocity of your load.

I believe that will give you the most accurate calculations for what is, after all, theoretical information. Now that I have gotten Ballistic into agreement with JBM (see previous post) I can use it more reliably as a tool out at the range and even adjust for temperature and altitude if need be. I'll be posting more after my next trip target shooting. Last time there were too many variables because of load testing, etc. to do any field testing of my drop tables.
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