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Old 04-01-2017, 06:30 PM   #6
Doctor of GURPS Ballistics
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Join Date: Sep 2004
Location: Burnsville, MN
Default Re: GURPS ULTRATECH ballistics?

Originally Posted by hal View Post
The goal I think, is to get an "average damage value" which does factor in velocity squared. The divisor of 450395 is likely a conversion factor between imperial units and metrics. I'm going to have to find the original spreadsheet Doug gave me to confirm.
Likely. There are a lot of funky units at play here. Grains, grams, pounds . . .

What I didn't understand in Doug's sheet were the metrics of 1/2 damage, etc and expansion of gases etc.

Hopefully, Doug himself will chime in on this, because I dimly recall I confirmed my formula with him before going with it...

Catch you in about 60 to 90 minutes
The 1/2D calculations used an exponential fall off of velocity based on sectional density. It's close enough to give a good approximation in the supersonic regime but isn't nearly as good as a real ballistics table.

the gas expansion stuff is just a representation of how much energy goes into the bullet, based on integrating force over distance. I used the ideal gas law to figure out how the pressure falls off as the volume expands (the volume is the chamber plus the barrel) and then just integrated Force = Pressure x bullet area over the barrel length.

Expansion is something I just plug into my penetration and wound channel equation - increase bullet caliber by the expansion ratio, and let the rest take care of itself.

For basic bullets thrown from ultra-tech guns, you're doing the right idea - take best guesses for caliber, mass, and velocity, and adjust mass and velocity so they're not crazy-town and the damage is about right. The assumptions going into UT were not all rational and logical and if A then B, so it might not work every time.
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