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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Does velocity affect ballistic coefficient?
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<blockquote data-quote="Blackdirt Cowboy" data-source="post: 2274111" data-attributes="member: 108138"><p>I loaded up a load for my 7 rum using 145 grain hammers. Average velocity of this round is 3635 FPS over 12-15 rounds fired over a magnetospeed. I zeroed the load at 200 yards and entered all the data into my ballistic calculator and went out to shoot steel and verify drops. I used a bc of .230 as indicated on hammers website, which they said was verified by drops, not estimated.</p><p></p><p>At 415 yards, I was about 1 1/4" high. Not too bad, so I backed off to 525 yards and was 3" high. When I got back home, I started making adjustments to the bc in the calculator. When I entered it as .320, it's dead on with the results I saw on the steel plate.</p><p></p><p>I know my velocity numbers are good, as the SD of my load was single digits and the ES was around 13. I also measured the sight height, so that's not giving me any issues either. The only thing "unknown" is the bc. Is it common to have to adjust the bc that far from the advertised bc? I know this is a pretty fast load, so maybe that has something to do with it? What are y'all's thoughts?</p></blockquote><p></p>
[QUOTE="Blackdirt Cowboy, post: 2274111, member: 108138"] I loaded up a load for my 7 rum using 145 grain hammers. Average velocity of this round is 3635 FPS over 12-15 rounds fired over a magnetospeed. I zeroed the load at 200 yards and entered all the data into my ballistic calculator and went out to shoot steel and verify drops. I used a bc of .230 as indicated on hammers website, which they said was verified by drops, not estimated. At 415 yards, I was about 1 1/4” high. Not too bad, so I backed off to 525 yards and was 3” high. When I got back home, I started making adjustments to the bc in the calculator. When I entered it as .320, it’s dead on with the results I saw on the steel plate. I know my velocity numbers are good, as the SD of my load was single digits and the ES was around 13. I also measured the sight height, so that’s not giving me any issues either. The only thing “unknown” is the bc. Is it common to have to adjust the bc that far from the advertised bc? I know this is a pretty fast load, so maybe that has something to do with it? What are y’all’s thoughts? [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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Does velocity affect ballistic coefficient?
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