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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
??? for JBM.
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<blockquote data-quote="JBM" data-source="post: 32337" data-attributes="member: 1969"><p>If it's published by Sierra, it's going to be a G1. I've never seen them publish anything else.</p><p></p><p>On my website in the downloads section there is a file that is a reprint of some drag functions from "Exterior Ballistics of Small Arms Projectiles". At 2600 f/s, you can see that the G1 drag function is 0.2959 and 0.1869. Since G1/BC1 = G5/BC5 (the CD of the bullet is the same, so these terms have to be the same for the same atmospheric conditions) so BC5 = BC1 * G5/G1 = 0.450 * (0.1869/0.2959) = 0.284.</p><p></p><p>Now if you run two trajectories, one with the G1 BC and the other with the G5 BC you can see they are pretty close (it convinces me that I didn't mess up the math). They aren't exactly the same though because we used only one BC at one velocity.</p></blockquote><p></p>
[QUOTE="JBM, post: 32337, member: 1969"] If it's published by Sierra, it's going to be a G1. I've never seen them publish anything else. On my website in the downloads section there is a file that is a reprint of some drag functions from "Exterior Ballistics of Small Arms Projectiles". At 2600 f/s, you can see that the G1 drag function is 0.2959 and 0.1869. Since G1/BC1 = G5/BC5 (the CD of the bullet is the same, so these terms have to be the same for the same atmospheric conditions) so BC5 = BC1 * G5/G1 = 0.450 * (0.1869/0.2959) = 0.284. Now if you run two trajectories, one with the G1 BC and the other with the G5 BC you can see they are pretty close (it convinces me that I didn't mess up the math). They aren't exactly the same though because we used only one BC at one velocity. [/QUOTE]
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