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new twist on b.c.'s
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<blockquote data-quote="JBM" data-source="post: 11988" data-attributes="member: 1969"><p><strong>Re: new twist on b.c.\'s</strong></p><p></p><p><BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>I'm afraid I don't quite understand. Can you elaborate? I don't know if it is apples and oranges because the Oehler model 43 acoustic chronograph comes with software to calculate bc's clear out to 1000 yards.</p><p><HR></BLOCKQUOTE></p><p></p><p>I'm sure it can. I was just commenting that if you calculate a BC with velocities measured at the muzzle and 500 yards, you get an average (weighted) BC for that velocity range. This may not be the velocity range that the manufacturers use so the BC may be different. That's not to say that either are incorrect, just different. -- it's hard to know what the manufacturer did. </p><p></p><p> <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>It seems bc's can be calculated at any range even though Sierra does their's at 300 meters and JBM's website calculates at 200 yards. <HR></BLOCKQUOTE></p><p></p><p>That's up to 200 yards. If I were doing it (and I will be when I build my chronograph for measuring BCs) I would get multiple BC measurements at different velocities instead of getting an average over long velocities. Actually, I want to measure CD anyway... I don't really care about BCs.</p><p></p><p> <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>I remember reading an article in a Precision Shooter magazine some years ago about a group of guys who tested many of the popular vld's at 1000 yards with the help of 2 Oehler model 43's. (wouldn't that be nice!). It showed that the majority of the tested bullets actually IMPROVED the farther downrange they went.<HR></BLOCKQUOTE></p><p></p><p>That wouldn't surprise me. The pitching and yawing should dampen as the bullets go down range leading to a lower effective CD (and higher BC). Typically the CD is CD0 + d^2*CDd2 where d is sin^2(a) and a is the angle of attack. So as a lessens, CD should go down and BC up. Did they say how much it changed?</p><p></p><p> <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> It intrigued Dr. Oehler so much that he even flew out to the range to get in on the experiment himself firsthand! So that led me to conclude that it might help to chrono at 500 yards instead of 200 so I would get a little more accurate read.<HR></BLOCKQUOTE></p><p></p><p>That's fine, but if you only measure one velocity at 500 yards, and one at the muzzle, your measure BC is an average of everything that happend from the muzzle to 500 yards. I'd be more interested in the numbers if you measured 2 velocities at 500 yards and calculated the BC there.</p><p></p><p> <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Also, are you "THE" JBM of JBM Ballistics?<HR></BLOCKQUOTE></p><p></p><p>Yes.</p></blockquote><p></p>
[QUOTE="JBM, post: 11988, member: 1969"] [b]Re: new twist on b.c.\'s[/b] <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>I'm afraid I don't quite understand. Can you elaborate? I don't know if it is apples and oranges because the Oehler model 43 acoustic chronograph comes with software to calculate bc's clear out to 1000 yards. <HR></BLOCKQUOTE> I'm sure it can. I was just commenting that if you calculate a BC with velocities measured at the muzzle and 500 yards, you get an average (weighted) BC for that velocity range. This may not be the velocity range that the manufacturers use so the BC may be different. That's not to say that either are incorrect, just different. -- it's hard to know what the manufacturer did. <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>It seems bc's can be calculated at any range even though Sierra does their's at 300 meters and JBM's website calculates at 200 yards. <HR></BLOCKQUOTE> That's up to 200 yards. If I were doing it (and I will be when I build my chronograph for measuring BCs) I would get multiple BC measurements at different velocities instead of getting an average over long velocities. Actually, I want to measure CD anyway... I don't really care about BCs. <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>I remember reading an article in a Precision Shooter magazine some years ago about a group of guys who tested many of the popular vld's at 1000 yards with the help of 2 Oehler model 43's. (wouldn't that be nice!). It showed that the majority of the tested bullets actually IMPROVED the farther downrange they went.<HR></BLOCKQUOTE> That wouldn't surprise me. The pitching and yawing should dampen as the bullets go down range leading to a lower effective CD (and higher BC). Typically the CD is CD0 + d^2*CDd2 where d is sin^2(a) and a is the angle of attack. So as a lessens, CD should go down and BC up. Did they say how much it changed? <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> It intrigued Dr. Oehler so much that he even flew out to the range to get in on the experiment himself firsthand! So that led me to conclude that it might help to chrono at 500 yards instead of 200 so I would get a little more accurate read.<HR></BLOCKQUOTE> That's fine, but if you only measure one velocity at 500 yards, and one at the muzzle, your measure BC is an average of everything that happend from the muzzle to 500 yards. I'd be more interested in the numbers if you measured 2 velocities at 500 yards and calculated the BC there. <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Also, are you "THE" JBM of JBM Ballistics?<HR></BLOCKQUOTE> Yes. [/QUOTE]
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