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Old 09-28-2017, 07:40 AM   #63
Doctor of GURPS Ballistics
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Join Date: Sep 2004
Location: Burnsville, MN
Default Re: GURPS ULTRATECH ballistics?

Originally Posted by mlangsdorf View Post
I stole this from Doug's spreadsheet:
volume in cubic cm = (PI*(Bore/2)^3 + PI/12*Bore^2*(2*Bore*Aspect Ratio-Bore)) / 1000

where bore is bullet bore in milliimeters and aspect ratio is bullet length / bullet bore.
what this is supposed to be - and I'm too tired to really check it right now - is a cylindrical base equal to half the bore in height. That's pi x (Bore/2)^2 x Bore/2, which of course is pi x (Bore/2)^3.

Then it adds in an ellipsoid of revolution, volume pi/6 x A^2 x C, and C is the Aspect Ratio x 2 x Bore. And we only need the top half. you get what's in the formula.

It's not perfect by any means, but if you look at the shapes produced, they look pretty close to what real bullets look like, and makes the density measurement not bad.
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