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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Light, high BC bullet
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<blockquote data-quote="Warren Jensen" data-source="post: 20884" data-attributes="member: 21"><p>Just for you information,</p><p></p><p>I spent about an hour on the computer last night, and the old phrase "You can't get there from here" applies.</p><p></p><p>The best I could get with an 80 gr. .308 bullet was a BC of .348. I kept increasing the ogive lengths and secant radii until I had a bullet that was 5.58" long with a 90 caliber secant radius. Because the volume kept getting larger I had to decrease the material density to keep the weight at 80 gr. That final bullet had a density of .050 lbs./ cubic inch, which is midway between nylon and aluminum. It also required a twist of 1 full turn in 1.5 inches to be stable, which is more like thread pitch than rifling. It would require some multi-increment gain twist to get an exit spin that fast. </p><p></p><p>The reason I stopped was that as the volume increased so did the surface area, and as I was decreasing the form drag by lengthening the ogive I was increasing the friction drag due to the added surface area. Further increases in the ogive resulted in the BC starting down.</p><p></p><p>So there it is. The best BC I could get with an 80 gr., .308 was .348. To get a higher BC would required more weight or going subcaliber and putting it in a sabot.</p></blockquote><p></p>
[QUOTE="Warren Jensen, post: 20884, member: 21"] Just for you information, I spent about an hour on the computer last night, and the old phrase "You can't get there from here" applies. The best I could get with an 80 gr. .308 bullet was a BC of .348. I kept increasing the ogive lengths and secant radii until I had a bullet that was 5.58" long with a 90 caliber secant radius. Because the volume kept getting larger I had to decrease the material density to keep the weight at 80 gr. That final bullet had a density of .050 lbs./ cubic inch, which is midway between nylon and aluminum. It also required a twist of 1 full turn in 1.5 inches to be stable, which is more like thread pitch than rifling. It would require some multi-increment gain twist to get an exit spin that fast. The reason I stopped was that as the volume increased so did the surface area, and as I was decreasing the form drag by lengthening the ogive I was increasing the friction drag due to the added surface area. Further increases in the ogive resulted in the BC starting down. So there it is. The best BC I could get with an 80 gr., .308 was .348. To get a higher BC would required more weight or going subcaliber and putting it in a sabot. [/QUOTE]
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Light, high BC bullet
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