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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Calculating BC with LabRadar. It works!
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<blockquote data-quote="ptosis" data-source="post: 2355023" data-attributes="member: 116258"><p>Yep.</p><p></p><p>Indeed, knowing QNH and alt., it is possible to calculate QFE.</p><p></p><p>For the sake of completeness, there are several, more or less erroneous, pressure reduction formulae (cf. <a href="https://www.wmo.int/pages/prog/www/IMOP/meetings/SI/ET-Stand-1/Doc-10_Pressure-red.pdf" target="_blank">https://www.wmo.int/pages/prog/www/IMOP/meetings/SI/ET-Stand-1/Doc-10_Pressure-red.pdf</a>), but for shooting applications the error is typically negligible (most of the time, pocket barometers just interpolate QNH from standard atmosphere tables).</p><p></p><p>In practice, however, if I don't have a barometer at hand, I just pull the QFF (where real conditions on site are used for the correction rather than ISO standard conditions) from the nearest Meteosuisse station, take the difference as compared to the standard 1013.25, and apply the same difference to the standard pressure for the altitude I am at. When compared to Kestrel station pressure readings, the difference is within 2 Hpa (and I am not even sure which one is more precise), so for all practical purposes this works just fine.</p><p></p><p>The biggest source of errors when converting QNH to QFE is altitude. Altitude should be taken at the shooting station (using GPS or a detailed map). As practice shows when walking (or driving) up and down the mountain slopes, pressure-based altimeters can drift away pretty significantly.</p></blockquote><p></p>
[QUOTE="ptosis, post: 2355023, member: 116258"] Yep. Indeed, knowing QNH and alt., it is possible to calculate QFE. For the sake of completeness, there are several, more or less erroneous, pressure reduction formulae (cf. [URL]https://www.wmo.int/pages/prog/www/IMOP/meetings/SI/ET-Stand-1/Doc-10_Pressure-red.pdf[/URL]), but for shooting applications the error is typically negligible (most of the time, pocket barometers just interpolate QNH from standard atmosphere tables). In practice, however, if I don't have a barometer at hand, I just pull the QFF (where real conditions on site are used for the correction rather than ISO standard conditions) from the nearest Meteosuisse station, take the difference as compared to the standard 1013.25, and apply the same difference to the standard pressure for the altitude I am at. When compared to Kestrel station pressure readings, the difference is within 2 Hpa (and I am not even sure which one is more precise), so for all practical purposes this works just fine. The biggest source of errors when converting QNH to QFE is altitude. Altitude should be taken at the shooting station (using GPS or a detailed map). As practice shows when walking (or driving) up and down the mountain slopes, pressure-based altimeters can drift away pretty significantly. [/QUOTE]
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Calculating BC with LabRadar. It works!
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