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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
BEWARE, Problems with Exbal and G7 BC's
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<blockquote data-quote="BryanLitz" data-source="post: 447782" data-attributes="member: 7848"><p>I have a thought.</p><p></p><p>One of the most difficult things to keep straight with ballistics programs, both for the programmers and users, is the distinction between station pressure, corrected pressure, and altitude. I'll skip the full explanation, it can be found elsewhere on this forum. To the point, if the station pressure is entered as (or the program interprets it as) a corrected pressure, and you enter an altitude above sea level, the program will essentially double the effects of altitude. In other words, you give it a station pressure of 26.62". If the program considers that as a corrected-to-sea-level pressure, it will now find out what the station pressure is at 3250' (will be something like 23.?"). Now this false pressure which is too low is used to calculate the air density that the bullet is flying thru. In essence the program is flying the bullet at more than double the altitude you intended.</p><p></p><p>Your last case (the G7 prediction that is super flat) appears to be a symptom of this problem. My advice is to re-run the scenarios, paying specific attention to the pressure and altitude input. I'm not familiar with exbal so I don't know how the interface works, but with JBM, there's just a checkbox that says corrected pressure (or something like that). Having this checkbox checked can be the subtle difference between a correct trajectory calculation and a bad one. It can be easy to miss.</p><p></p><p>If you're doing everything correct on the inputs, it's possible that the error is behind the scenes. In other words the program isn't applying the inputs properly. Nothing against Gerald, anyone can make mistakes.</p><p></p><p>Does exbal display anywhere the air density that's being used for the calculation? I find this is extremely valuable information when troubleshooting ballistics programs. My programs and JBM display the air density which you can use to make sure that the result of your atmospheric inputs are being interpreted as you intended. This allows you to compare ballistics programs in a fair 'apples-to-apples' manner.</p><p></p><p>I'm sure the problem stems from atmospherics, not the fact that a G7 BC is being used.</p><p></p><p>Please let us know what you find out.</p><p></p><p>-Bryan</p></blockquote><p></p>
[QUOTE="BryanLitz, post: 447782, member: 7848"] I have a thought. One of the most difficult things to keep straight with ballistics programs, both for the programmers and users, is the distinction between station pressure, corrected pressure, and altitude. I'll skip the full explanation, it can be found elsewhere on this forum. To the point, if the station pressure is entered as (or the program interprets it as) a corrected pressure, and you enter an altitude above sea level, the program will essentially double the effects of altitude. In other words, you give it a station pressure of 26.62". If the program considers that as a corrected-to-sea-level pressure, it will now find out what the station pressure is at 3250' (will be something like 23.?"). Now this false pressure which is too low is used to calculate the air density that the bullet is flying thru. In essence the program is flying the bullet at more than double the altitude you intended. Your last case (the G7 prediction that is super flat) appears to be a symptom of this problem. My advice is to re-run the scenarios, paying specific attention to the pressure and altitude input. I'm not familiar with exbal so I don't know how the interface works, but with JBM, there's just a checkbox that says corrected pressure (or something like that). Having this checkbox checked can be the subtle difference between a correct trajectory calculation and a bad one. It can be easy to miss. If you're doing everything correct on the inputs, it's possible that the error is behind the scenes. In other words the program isn't applying the inputs properly. Nothing against Gerald, anyone can make mistakes. Does exbal display anywhere the air density that's being used for the calculation? I find this is extremely valuable information when troubleshooting ballistics programs. My programs and JBM display the air density which you can use to make sure that the result of your atmospheric inputs are being interpreted as you intended. This allows you to compare ballistics programs in a fair 'apples-to-apples' manner. I'm sure the problem stems from atmospherics, not the fact that a G7 BC is being used. Please let us know what you find out. -Bryan [/QUOTE]
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BEWARE, Problems with Exbal and G7 BC's
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