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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: 2539039" data-attributes="member: 1521"><p>Yes DA and PA are equal under standard conditions for altitude. And since standard conditions couldn't ever be relied on, the separate parameters must be measured -> for ballistics.</p><p></p><p>Those measured parameters can be used to calculate DA, but inside ballistic software, the individual parameters are better taken for their separate contributions to drag calcs & lookups. This, rather than forcing the software to rely solely on air density as a general term.</p><p>For instance, temperature and relative humidity affect Mach, and every lookup on a drag table is w/resp to Mach#. This individual attribute is independent of air density itself. So if you force software to set temperature based on DA, the Mach#s/Drag will be wrong all the way.</p><p>It won't affect a local G7 BC much, but it is another inaccuracy added.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 2539039, member: 1521"] Yes DA and PA are equal under standard conditions for altitude. And since standard conditions couldn't ever be relied on, the separate parameters must be measured -> for ballistics. Those measured parameters can be used to calculate DA, but inside ballistic software, the individual parameters are better taken for their separate contributions to drag calcs & lookups. This, rather than forcing the software to rely solely on air density as a general term. For instance, temperature and relative humidity affect Mach, and every lookup on a drag table is w/resp to Mach#. This individual attribute is independent of air density itself. So if you force software to set temperature based on DA, the Mach#s/Drag will be wrong all the way. It won't affect a local G7 BC much, but it is another inaccuracy added. [/QUOTE]
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Altitude vs. Barometric pressure
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