460-315-HP Ballistic coefficient

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2019-02-27 at 13:34 #489879
yah
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Recently bought 460-315-HP GC AV3 mold for my Texan SS. I’m wondering, how do I know the Ballistic coefficient?
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2019-02-27 at 17:19 #511625
rsterne
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The listed BC for that bullet is 0.263, on the drawing in the Store…. I think you may find that a bit high for Subsonic use in an airgun, I would use about 0.9 x the SD, which would be about 0.19….

Bob
2019-02-27 at 18:41 #511626
robertpedersen1
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If you fire the projectile over a chronograph at at least two distances (multiple times to get a good average), you can calculate the BC.

https://www.jbmballistics.com/cgi-bin/jbmbcv-5.1.cgi
https://www.sellier-bellot.cz/en/products/ballistic-coefficient-calculation/
(And more. Just search for “ballistic coefficient calculator” or “calculate ballistic coefficient”.)
2019-03-01 at 09:00 #511627
yah
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Thanks guys! I didn’t notice those numbers in the drawing.
My chronograph has a very small window for risk shooting at even 30 yards(
2019-03-01 at 17:03 #511628
rsterne
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At 30 yards with a big, heavy bullet, you probably would not get enough velocity drop to consistently allow you to calculate the BC…. You might be better off to use trajectory…. sight the gun at 50 yards, shoot it at 100 and measure the drop…. then use ChairGun to calculate the BC…. Determining accurately the POI of the group is the most difficult part…. as only a small error will change the BC drastically….

Bob
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