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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Let's argue about BC's
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<blockquote data-quote="groper" data-source="post: 480067" data-attributes="member: 12550"><p>LR3,</p><p>I pulled this from earlier in the thread,... dont forget to read the pdf files mike courtney posted to get the basic theory in your head, then check out my description/modification to the process disclosed below; - its almost as good as bryans method, provided you pay careful attention to the details...</p><p></p><p> Originally Posted by <strong>Michael Courtney</strong> <a href="http://www.longrangehunting.com/forums/f19/lets-argue-about-bcs-68234-post478192/#post478192" target="_blank"><img src="http://www.longrangehunting.com/forums/images/styles/longrangehunting/buttons/viewpost.gif" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a> </p><p> <em><u><strong>First of all, BCs should be measured with either the velocity loss or the time of flight technique.</strong></u> <u><strong>Using bullet drop is prone to many errors because bullet drop is sensitive to many uncertainties and confounding factors that do not exist at all or have much smaller effect on velocity loss and time of flight techniques.</strong></u></em></p><p> <em></em></p><p><em>Secondly, anyone who cares about BC accuracy and effects on retained velocity, wind drift, and drop should read Bryan Litz's book. </em></p><p> <em></em></p><p><em>We've published four papers on BC issues and acoustic measurement techniques:</em></p><p> <em></em></p><p><em><a href="http://arxiv.org/ftp/physics/papers/0601/0601102.pdf" target="_blank">http://arxiv.org/ftp/physics/papers/0601/0601102.pdf</a></em></p><p> <em></em></p><p><em><a href="http://arxiv.org/ftp/arxiv/papers/0812/0812.4752.pdf" target="_blank">http://arxiv.org/ftp/arxiv/papers/0812/0812.4752.pdf</a></em></p><p> <em></em></p><p><em><a href="http://arxiv.org/ftp/arxiv/papers/0705/0705.0391.pdf" target="_blank">http://arxiv.org/ftp/arxiv/papers/0705/0705.0391.pdf</a></em></p><p> <em></em></p><p><em><a href="http://arxiv.org/ftp/arxiv/papers/0705/0705.0389.pdf" target="_blank">http://arxiv.org/ftp/arxiv/papers/0705/0705.0389.pdf</a></em></p><p> <em></em></p><p><em>Even though we've validated an acoustic technique with simultaneous use of near and far chronographs, the two chronograph method is more accurate and highly recommended where possible, because small errors in various measurements (near velocity, distance, temperature, air pressure, etc.) have smaller impact on BC determinations with two chronographs. </em></p><p> <em></em></p><p><em>In our two chronograph method, we verify that the two chronographs give the expected velocity drop (1-4 fps) when placed a few feet apart before we extend the distance to 300 or 600 feet.</em></p><p> <em></em></p><p><em>We have seen significant variances in BCs between different rifles, and even within the same rifle before and after polishing the bore. Lots of factors effect bullet drag. In the absence of a BC measurement in a specific rifle, Bryan Litz's numbers are usually the best available estimate, but I strongly prefer to measure the BC in my rifle using two chronographs spaced by 300-600 feet. A single chronograph and our acoustic technique for your specific rifle would also be preferable to just going with any published number. In contrast, you're probably better off going with a published number than with a BC estimate determined from drop.</em></p><p> <em></em></p><p><em>Michael Courtney</em></p></blockquote><p></p>
[QUOTE="groper, post: 480067, member: 12550"] LR3, I pulled this from earlier in the thread,... dont forget to read the pdf files mike courtney posted to get the basic theory in your head, then check out my description/modification to the process disclosed below; - its almost as good as bryans method, provided you pay careful attention to the details... Originally Posted by [B]Michael Courtney[/B] [URL="http://www.longrangehunting.com/forums/f19/lets-argue-about-bcs-68234-post478192/#post478192"][IMG]http://www.longrangehunting.com/forums/images/styles/longrangehunting/buttons/viewpost.gif[/IMG][/URL] [I][U][B]First of all, BCs should be measured with either the velocity loss or the time of flight technique.[/B][/U] [U][B]Using bullet drop is prone to many errors because bullet drop is sensitive to many uncertainties and confounding factors that do not exist at all or have much smaller effect on velocity loss and time of flight techniques.[/B][/U] Secondly, anyone who cares about BC accuracy and effects on retained velocity, wind drift, and drop should read Bryan Litz's book. We've published four papers on BC issues and acoustic measurement techniques: [URL]http://arxiv.org/ftp/physics/papers/0601/0601102.pdf[/URL] [URL]http://arxiv.org/ftp/arxiv/papers/0812/0812.4752.pdf[/URL] [URL]http://arxiv.org/ftp/arxiv/papers/0705/0705.0391.pdf[/URL] [URL]http://arxiv.org/ftp/arxiv/papers/0705/0705.0389.pdf[/URL] Even though we've validated an acoustic technique with simultaneous use of near and far chronographs, the two chronograph method is more accurate and highly recommended where possible, because small errors in various measurements (near velocity, distance, temperature, air pressure, etc.) have smaller impact on BC determinations with two chronographs. In our two chronograph method, we verify that the two chronographs give the expected velocity drop (1-4 fps) when placed a few feet apart before we extend the distance to 300 or 600 feet. We have seen significant variances in BCs between different rifles, and even within the same rifle before and after polishing the bore. Lots of factors effect bullet drag. In the absence of a BC measurement in a specific rifle, Bryan Litz's numbers are usually the best available estimate, but I strongly prefer to measure the BC in my rifle using two chronographs spaced by 300-600 feet. A single chronograph and our acoustic technique for your specific rifle would also be preferable to just going with any published number. In contrast, you're probably better off going with a published number than with a BC estimate determined from drop. Michael Courtney[/I] [/QUOTE]
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