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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Altitude vs. Barometric pressure
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<blockquote data-quote="Mikecr" data-source="post: 136773" data-attributes="member: 1521"><p>Looks like Tubb/S&amp;B has generated interest in use of Density Altitude as a single air density input in the field. Might work ok, I'll have to try it.</p><p>It is easy to figure and graph for one bullet. More difficult for the rest of the world.</p><p>Here we go:</p><p></p><p>Air Density(Kg/m3) from DA =</p><p>((3280.84*44.3308-<strong>DA</strong>)/(3280.84*42.2665))^(1/0.234969)</p><p>Air Density ratio(<strong>Ro</strong>) to ICAO conditions would equal the air density above <strong>divided by 1.225</strong> </p><p> <strong>Local BC</strong> would be ICAO <strong>BC/Ro</strong></p><p></p><p>Now Std Metro is less pretty because it's meaningless to the rest of the world. </p><p>Std Metro BCs COULD be(and really should be) normalized to ICAO BCs by [StdMetro BC*.982].</p><p>Or the density altitude formula above could be biased to account for a zero under StdMetro conditions by adding 625 to DA: ((3280.84*44.3308-(DA+625))/(3280.84*42.2665))^(1/0.234969), adjusting air density.</p><p>Then figure Ro = [StdMetro Air Density/1.20275]</p><p>And Local BC = [StdMetro BC/Ro]</p><p></p><p>Some seek a 'rule of thumb' for density altitude and drop table adjustments. But any rule of thumb would be specific to your BC as adjusted above and as washed through ballistic software for affects in the field.</p><p>Only then could these affects could be defined with a 'rule' or named something like 'DTAC'.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 136773, member: 1521"] Looks like Tubb/S&B has generated interest in use of Density Altitude as a single air density input in the field. Might work ok, I'll have to try it. It is easy to figure and graph for one bullet. More difficult for the rest of the world. Here we go: Air Density(Kg/m3) from DA = ((3280.84*44.3308-[b]DA[/b])/(3280.84*42.2665))^(1/0.234969) Air Density ratio([b]Ro[/b]) to ICAO conditions would equal the air density above [b]divided by 1.225[/b] [b]Local BC[/b] would be ICAO [b]BC/Ro[/b] Now Std Metro is less pretty because it's meaningless to the rest of the world. Std Metro BCs COULD be(and really should be) normalized to ICAO BCs by [StdMetro BC*.982]. Or the density altitude formula above could be biased to account for a zero under StdMetro conditions by adding 625 to DA: ((3280.84*44.3308-(DA+625))/(3280.84*42.2665))^(1/0.234969), adjusting air density. Then figure Ro = [StdMetro Air Density/1.20275] And Local BC = [StdMetro BC/Ro] Some seek a 'rule of thumb' for density altitude and drop table adjustments. But any rule of thumb would be specific to your BC as adjusted above and as washed through ballistic software for affects in the field. Only then could these affects could be defined with a 'rule' or named something like 'DTAC'. [/QUOTE]
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