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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Labrador vs ballistics chart speeds
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<blockquote data-quote="Mikecr" data-source="post: 1739160" data-attributes="member: 1521"><p>Temperature, Absolute Pressure(station pressure), and Relative Humidity are the parameters from which <strong>air density</strong> is calculated. Where you don't have measure of these you can alternately enter altitude and the software would lookup 'standard conditions' for altitude. But what then do you enter for the fields which would otherwise lead to calculating actual air density?</p><p>That's where some software allows Density Altitude entry, which should override all other fields. But many folks get this all confused with altitude, or pressure altitude, and they forget that DA is calculated from what you had to measure and enter anyway (Temperature, Absolute pressure(station pressure), and Relative Humidity.)..</p><p></p><p>Now if all you have is 'barometric pressure', which is sea level corrected, and as reported by airports, then(only then) you would have to assign the altitude that pressure is adjusted to. This, so that your software can back calculate absolute pressure, so that it can figure out air density.</p><p></p><p>I can recalculate drag and form factor for different conditions to adjust G1BC or G7BC instead of having ballistic software do this (like if it was weak in this function).</p><p>For instance, this .387 G7BC bullet (at ICAO and assumed 2850fps) has a local G7BC of .379 at 34degF, 0%Rh, and 29.96"Hg sea level corrected at 925' ASL.</p><p>But some software tracks w/resp to Mach #, and this is affected by the same air density parameters, so again the parameters really need to be entered explicitly.</p><p></p><p>This is the stuff most folks get befuddled on with ballistic software entries. It's hard to remember. So we should forget ALTITUDE,, and <u>think</u> AIR DENSITY (what matters).</p><p>Easiest to do this is simply measure the direct parameters needed by your software for air density. Temperature, Absolute pressure(station pressure), and Relative Humidity. Leave all other trickery at zero.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 1739160, member: 1521"] Temperature, Absolute Pressure(station pressure), and Relative Humidity are the parameters from which [B]air density[/B] is calculated. Where you don't have measure of these you can alternately enter altitude and the software would lookup 'standard conditions' for altitude. But what then do you enter for the fields which would otherwise lead to calculating actual air density? That's where some software allows Density Altitude entry, which should override all other fields. But many folks get this all confused with altitude, or pressure altitude, and they forget that DA is calculated from what you had to measure and enter anyway (Temperature, Absolute pressure(station pressure), and Relative Humidity.).. Now if all you have is 'barometric pressure', which is sea level corrected, and as reported by airports, then(only then) you would have to assign the altitude that pressure is adjusted to. This, so that your software can back calculate absolute pressure, so that it can figure out air density. I can recalculate drag and form factor for different conditions to adjust G1BC or G7BC instead of having ballistic software do this (like if it was weak in this function). For instance, this .387 G7BC bullet (at ICAO and assumed 2850fps) has a local G7BC of .379 at 34degF, 0%Rh, and 29.96"Hg sea level corrected at 925' ASL. But some software tracks w/resp to Mach #, and this is affected by the same air density parameters, so again the parameters really need to be entered explicitly. This is the stuff most folks get befuddled on with ballistic software entries. It's hard to remember. So we should forget ALTITUDE,, and [U]think[/U] AIR DENSITY (what matters). Easiest to do this is simply measure the direct parameters needed by your software for air density. Temperature, Absolute pressure(station pressure), and Relative Humidity. Leave all other trickery at zero. [/QUOTE]
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