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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
ballistic coefficient on bullets
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<blockquote data-quote="CatShooter" data-source="post: 130732" data-attributes="member: 7"><p>Actually... Mike and Roy are both on to it.</p><p></p><p>Back in the days when I was a young grasshopper, BC was determined by the famous "Dupont chart", which I still have a copy. It is a large wall chart that has figures of bullets, and some basic numbers, and you add or subtract points for certin features - you add for a boat tail, you subtract for a round nose. etc... it decorates my loading room now - I LOVE IT! /ubbthreads/images/graemlins/wink.gif</p><p></p><p>There are several protocols for determining BC... Sierra came out with their ballistic program many years ago (15-ish??), and it is sooooo bad, that each bullet has to be tested at many velocities, and different numbers assigned to it, so the program will reasonable track.</p><p></p><p>It is BADD SOFTWARE. But you can be reasonable sure that your Sierra bullet will track as predicted (but not always).</p><p></p><p>But it will not do a very good job of tracking other company's bullets.</p><p></p><p>Other companies measure the lost speed over a fixed distance (usually 200 yds) and give the bullet a fixed BC based on the lost velocity over that one tract at that one muzzle velocity.</p><p></p><p>There are sophisticated programs that will compute the BC and do the alterations BC as the bullet speed changes... </p><p></p><p>All these programs start at standard "mets".</p><p></p><p>The barometric pressure and the temperature are two variables that don't affect the BC, but the formula's must adjust for, because they affect the density of the air.</p><p></p><p>There are some bullet companies that STILL use the Dupont chart to rate their bullets.</p><p></p><p>So bullet "A" with a BC of .375 is NOT the same as bullet "B" or "C" or "D" with a BC of .375.</p><p></p><p>So it's kinda foggy... but I don't think we want the bullet police to come in and regulate it.</p><p></p><p>.</p></blockquote><p></p>
[QUOTE="CatShooter, post: 130732, member: 7"] Actually... Mike and Roy are both on to it. Back in the days when I was a young grasshopper, BC was determined by the famous "Dupont chart", which I still have a copy. It is a large wall chart that has figures of bullets, and some basic numbers, and you add or subtract points for certin features - you add for a boat tail, you subtract for a round nose. etc... it decorates my loading room now - I LOVE IT! [img]/ubbthreads/images/graemlins/wink.gif[/img] There are several protocols for determining BC... Sierra came out with their ballistic program many years ago (15-ish??), and it is sooooo bad, that each bullet has to be tested at many velocities, and different numbers assigned to it, so the program will reasonable track. It is BADD SOFTWARE. But you can be reasonable sure that your Sierra bullet will track as predicted (but not always). But it will not do a very good job of tracking other company's bullets. Other companies measure the lost speed over a fixed distance (usually 200 yds) and give the bullet a fixed BC based on the lost velocity over that one tract at that one muzzle velocity. There are sophisticated programs that will compute the BC and do the alterations BC as the bullet speed changes... All these programs start at standard "mets". The barometric pressure and the temperature are two variables that don't affect the BC, but the formula's must adjust for, because they affect the density of the air. There are some bullet companies that STILL use the Dupont chart to rate their bullets. So bullet "A" with a BC of .375 is NOT the same as bullet "B" or "C" or "D" with a BC of .375. So it's kinda foggy... but I don't think we want the bullet police to come in and regulate it. . [/QUOTE]
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ballistic coefficient on bullets
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