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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Help with BC calculation
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<blockquote data-quote="chessman" data-source="post: 35219" data-attributes="member: 2451"><p>First, I apologize to the group if my post last night came off as arrogant. I'm not a ballistics expert and have never claimed to be. I did want to establish some credibility as a physicist. What I do know is high-speed aerodynamics.</p><p></p><p>Dissect Jerry's original post. He knows the mass of the bullet and muzzle velocity, and he has measured the change in velocity over time by measuring the drop. Now he is looking for the math that describes the arc that the bullet flies – effectively, the equation that describes the aerodynamic drag on that particular bullet fired from that particular barrel. We don't know enough of the variables to make any absolute statements about BC or drag function. We still don't know the scope height, atmospheric conditions, or rate of twist.</p><p></p><p>The G1 function isn't a bad choice for the tangent ogive bullets of yesteryear. Those bullets all had the same basic shape and produced the same relative drag. The new secant ogive bullets do not have the same drag, so using one drag function for all bullets will not give accurate results for all bullets. If the G7 gives a closer match to the measured results, then why would we not use it for this bullet? </p><p></p><p>I still say the G7 function is a closer match to the observed results – maybe not perfect, but closer than G1. </p><p></p><p>If the equation doesn't match the results, then something is wrong with the equation.</p></blockquote><p></p>
[QUOTE="chessman, post: 35219, member: 2451"] First, I apologize to the group if my post last night came off as arrogant. I’m not a ballistics expert and have never claimed to be. I did want to establish some credibility as a physicist. What I do know is high-speed aerodynamics. Dissect Jerry’s original post. He knows the mass of the bullet and muzzle velocity, and he has measured the change in velocity over time by measuring the drop. Now he is looking for the math that describes the arc that the bullet flies – effectively, the equation that describes the aerodynamic drag on that particular bullet fired from that particular barrel. We don’t know enough of the variables to make any absolute statements about BC or drag function. We still don’t know the scope height, atmospheric conditions, or rate of twist. The G1 function isn’t a bad choice for the tangent ogive bullets of yesteryear. Those bullets all had the same basic shape and produced the same relative drag. The new secant ogive bullets do not have the same drag, so using one drag function for all bullets will not give accurate results for all bullets. If the G7 gives a closer match to the measured results, then why would we not use it for this bullet? I still say the G7 function is a closer match to the observed results – maybe not perfect, but closer than G1. If the equation doesn’t match the results, then something is wrong with the equation. [/QUOTE]
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Help with BC calculation
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