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Ballistic Program Inconsistencies

 
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  #1  
Old 09-07-2009, 09:48 AM
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Ballistic Program Inconsistencies

Over the past 5 years I have began to really become involved in long range shooting/hunting. I have over the years used various ballistic software and find that each has its pros and cons as you would suspect.

What I cannot understand is why these programs give varying trajectory information -- some being very close to where the bullet actually struck with the given conditions, some being in the general area of being right and some that I have tried are up to 13 inches off. My question is, how can there be so many ballistic programs and each gives much different drop information?

It seems to me that just like with math, especially with physics that if you input the right information you get the right information out. 2+2 is always 4 and yet it seems that despite that fact ballistic programs still vary drastically in their output information. We all know that of the varying equations used and theories (for example between the work of Mccoy and Pejsa etc) that only one will be correct and that is proven when the bullet strikes the paper. It would seem only logical to me that researchers would have built upon eachothers work and came up with equations that accurately depict where the bullet will strike, afteral, it is only math right?

So why are there so many programs out there giving wrong information and using wrong data whhen we know there is the right data out there?

Help clear up my confusion... please!

Kyle
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Old 09-08-2009, 07:36 AM
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Re: Ballistic Program Inconsistencies

Kyle,
There are many reasons why programs can give slightly different answers, but few reasons why they may give drastically different answers.

Here's a list of some things that come to mind:
Solution method. Certain simplifications of the math are made in some solution methods to get to an answer. The Siacci and Pejsa solutions are examples of solution methods that use 'short-cuts' to get to an answer. These short cuts are usually not very costly in terms of accuracy. The Pejsa solution doesn't interpret BC the way other programs do. Solutions that use numerical integration (point mass solutions) will compromise the least accuracy.

Atmosphere. There are two definitions of the 'standard' atmosphere in common use: Army Standard Metro (ASM) and ICAO (something like: International Civil Aviation Administration). Some programs use one, some the other. BC's are also defined by one or the other. One possible error is to use a BC that's defined based on ASM in a program that uses ICAO or vise versa. This will introduce an effective error of 1.7% in the BC (or air density) that you're using.

Of course there is user error to consider. If the inputs are misleading or unclear, one could accidentally enter inconsistent information.

My advice is to check whatever program you use against the JBM online ballistics program. JBM uses a point mass solver, and is extremely accurate. You can tell how accurate your program is by seeing how well it compares to JBM.

-Bryan
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Bryan Litz
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Author of: Applied Ballistics for Long Range Shooting
And: Accuracy and Precision for Long Range Shooting

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Old 09-09-2009, 06:39 PM
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Re: Ballistic Program Inconsistencies

Hi Brian,

Thank you for the reply, I do see where you are coming from and the differences it would cause. I was just very surprised to see how some programs varied up to 13 inches in elevation for the same bullet and information. I do like JBM and wish that he would make it in pc format so that I could use it offline. In pda version would also be a huge plus.

I will for now stick to using JBM as I have found it to be about the most accurate.


Thanks again!

Kyle
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Old 09-09-2009, 10:05 PM
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Re: Ballistic Program Inconsistencies

Kyle,
Out of curiosity, can you tell me what programs you were getting 13" of difference with? That seems like a lot and these kinds of things interest me.
Thanks,
-Bryan
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Bryan Litz
Ballistician

Author of: Applied Ballistics for Long Range Shooting
And: Accuracy and Precision for Long Range Shooting

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Old 09-10-2009, 12:03 PM
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Re: Ballistic Program Inconsistencies

Bryan,

I will compile a list of programs I used when I get home from work this evening. I can even send you the programs as some are no longer available. Do you know of any program that is comparable to the results of JBM in accuracy that I could use on my pc when I am not connected to the internet or on my pda? I am really looking for an accurate program for my pda using palm os.

Thanks again!

Kyle
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Old 09-10-2009, 12:19 PM
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Re: Ballistic Program Inconsistencies

Kyle,
The point mass ballistics program that comes with my book (Book) matches JBM within round off error (fraction of an inch) at ranges beyond 1000 yards. They're essentially the same solution written by different individuals which use the same atmosphere model.

There are several iPhone apps that can use G7 BC's. To my knowledge, the only one for windows based mobile devices is Loadbase 3. I'll be working on developing another program for mobile devices (Palm, blackberry, windows, etc) over the winter.

-Bryan
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Bryan Litz
Ballistician

Author of: Applied Ballistics for Long Range Shooting
And: Accuracy and Precision for Long Range Shooting

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  #7  
Old 09-10-2009, 02:29 PM
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Re: Ballistic Program Inconsistencies

Bryan,

I am very interested to read your book. I will have to save up some pennies -- times are still hard here in the Midwest. Your program sounds very appealing, while it for now will only work on a pc, I could atleast use it on the laptop while out punching paper -- something I cannot do with JBM.

Some of the programs I found that were way off are:

Ballistix - Based on Pejsa's work

BalCal

Excelbal - Jackson Rifle excel sheet based on Pejsa

Point Blank

Al Bal

Of the programs I have found to match very closely to JBM one stands out it is created by Derek Yates and is GNU Exterior Ballistics.

Hopefully soon, I will be able to order your new book, learn something new and use the ballistic calculator you have created.

Thank you for all of your replies Bryan!

Kyle
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