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Old 09-22-2017, 10:32 AM   #32
Join Date: Aug 2004
Location: Austin, TX
Default Re: Binary propellant and Standard TL 8 guns?

Google docs are easy to share:

You can't edit it, but you should be able to duplicate it and then edit the copy.

How it works:
You put the bullet diameter in mm in cell C1, bullet mass (in grams) in C2, muzzle velocity in m/s in C3, and the bullet aspect ratio* in H1.

The spreadsheet will take a guess for the coefficient of drag** and do a lot of math. Eventually, it will spit out the results in cells D6 to D9: 1/2d range and max range, for firing at a 10 degree angle (basically horizontal) and at a 45 degree angle (maximum possible range).

It uses 400 rows to calculate the first 4 seconds of travel time in 0.01 second increments, and uses another 600 rows to calculate the rest of the flight time. deltaT for those rows is variable based on muzzle speed, and you can scale the deltaT by putting a value in F10 ("DelTFudge"). The deltaT is based on the flight time of the projectile in a vacuum, so it's usually longer than necessary and you can usually shorten the deltaT to get more precise results.

By default, it calculates shots from 0 m above ground level, at 10 degrees and at 45 degrees. You can change the height and vary the angle with cells C5 and C4.

Cells P1-Z6 have some sample values for various projectiles, with the numbers for mass and muzzle velocity taken from wikipedia.

Compared to GURPS standard, pistol bullets have roughly 2x the 1/2d range, but 2/3rds the max range; rifles are with +/- 20%. Wikipedia and GURPS High-Tech disagree on a lot of those numbers, so I don't know.

* This is 1 for round shot like cannonballs, 2 for pistol bullets and shotgun slugs, and 3 or more for rifle bullets but see the note on coefficient of drag.
** Coefficient of drag varies with bullet shape and velocity. I'm assuming a static CoD based on the numbers from the wikipedia article and some rough curve fitting. You can adjust the CoD by putting a value in H10 ("CoD Fudge"). If anyone has better data on CoD I'd love to see it; I know you can theoretically do stuff with a ballistics coefficient but it's been a long, long time since fluid dynamics and I can't resolve the equations on wikipedia.
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