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BEWARE, Problems with Exbal and G7 BC's

 
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  #22  
Old 12-12-2010, 11:37 AM
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Re: BEWARE, Problems with Exbal and G7 BC's

Quote:
Originally Posted by bigngreen View Post
So we have three standards out there ICAO, ASM and SAA?
Unfortunately, yes.

Good news is that ICAO is used most of the time.

Also, the consequence of mis-matching the BC with the program is less than 2% error in BC, which only shows up at very long range.

-Bryan
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  #23  
Old 12-12-2010, 07:58 PM
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Re: BEWARE, Problems with Exbal and G7 BC's

I sent Mr. Perry from Exbal an email asking him what atmospheric standard Exbal uses. Here is his response:

"Eric;

ICAO has a sea level pressure 29.92 and by definition of ICAO it is bone dry air (ie no humidity). ASM has a sea level pressure of 29.53 and 78% humidity by definition. ASM is the standard set by US Army Aberdeen proving grounds long ago. Half of the vendors use ASM and half use ICAO. The statement that a BC value calculated for ICAO is different than a BC calculated for ASM is misleading. BC is the ratio of how far a given bullet travels in one second to how far the standard bullet travels in one second. This ratio will not change with ASM or ICAO. Trajectory calculations are a different matter. you can play with humidity and pressure at sea level and see the difference.



Exbal use default values of 29.92 pressure and 78% humidity at sea level so it is a hybrid solution.

Gerald L. Perry "
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  #24  
Old 12-12-2010, 08:14 PM
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Re: BEWARE, Problems with Exbal and G7 BC's

If you are going to quote him on line you should be courteous enough to tell him before hand that you are going to do so.

What you have just done is dishonest, cowardly and disgusting if you do not have his prior approval to post his reply.
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  #25  
Old 12-12-2010, 08:21 PM
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Re: BEWARE, Problems with Exbal and G7 BC's

Quote:
BC is the ratio of how far a given bullet travels in one second to how far the standard bullet travels in one second.
This is absolutely incorrect.

BC is defined as the Sectional Density (SD) of a bullet, divided by it's form factor referenced to a standard projectile. BC has units of lb/in^2.

In equation form:



Here is the rest of the Wiki article:
Ballistic coefficient - Wikipedia, the free encyclopedia

Other sources:
Modern Exterior Ballistics by Robert McCoy, page 101
Exterior Ballistics by George Klimi, page 46
Rifle Accuracy Facts by Harold Vaughn, page 203

I don't wish to engage Mr Perry, just wanting to share my information with others who are interested.

Interesting that he's using a 'hybrid' atmosphere. Given that fact, I have no idea how to properly adjust BC's for exbal.
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And: Accuracy and Precision for Long Range Shooting


Last edited by bsl135; 12-12-2010 at 08:27 PM.
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  #26  
Old 12-12-2010, 08:26 PM
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Re: BEWARE, Problems with Exbal and G7 BC's

Quote:
Originally Posted by Buffalobob View Post
If you are going to quote him on line you should be courteous enough to tell him before hand that you are going to do so.

What you have just done is dishonest, cowardly and disgusting if you do not have his prior approval to post his reply.
I disagree. Mr Perry was simply answering a customers question. Why would he answer any different with the knowledge that his reply would be 'peer reviewed'? Suggesting he might answer differently is suggesting... what?

I've seen my emails to individual customers quoted on forums many times. It's always done in places where others can benefit from the information and I've never had a problem with it. I'm actually grateful because it's a way to get the information out to many people so the question doesn't have to be answered as many times.

If he'd reveled any secrets, I would agree. But he just provided information about how his program works. That can only help his customers, right?
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  #27  
Old 12-12-2010, 08:45 PM
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Re: BEWARE, Problems with Exbal and G7 BC's

My older version of Exbal(7.1) defaults at standard metro(29.53, 59, 78%).
Doesn't make any sense that they/he would drop this for standard artillery, instead of ICAO.
I think he's made a mistake.
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  #28  
Old 12-12-2010, 09:05 PM
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Re: BEWARE, Problems with Exbal and G7 BC's

I am not sure how posting Mr Perry's response was is any way distasteful? People on this thread are interested in what model his software is using. His response to me answered that question and provides benefit to all who are using his software. I have been using Exbal for a long time and will continue to use it. Had he divulged information that was private or personal in any way I would not have posted it.
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