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Old 09-27-2017, 06:20 PM   #61
Anthony
 
Join Date: Feb 2005
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Default Re: GURPS ULTRATECH ballistics?

Quote:
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
For a bullet with a perfect half-sphere rounded tip:
Volume of tip = 2/3 * pi * r^3
Volume of cylinder = pi * r^2 * (length - r), or pi * r^3 * (aspect ratio*2 - 1)
where bore is bullet bore in milliimeters and aspect ratio is bullet length / bullet bore.

Accumulating variables, we get pi * r^3 * (AR*2 - 1/3), or pi*B^3*(AR/4 - 1/24).
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Old 09-27-2017, 08:28 PM   #62
Rupert
 
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Location: Wellington, NZ
Default Re: GURPS ULTRATECH ballistics?

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Originally Posted by mlangsdorf View Post
For rifle caliber bullets, 3G3 suggests roughly a 3:1:3 ratio of bullet mass to propellant mass to casing mass. A caseless round should weigh about 4/7ths an equivalent cased round - and when you consider that you're really evaluating TL6 cased rounds with moderate REF propellants versus TL8+ caseless rounds with higher REF propellants, you can get half the weight.
Except that caseless propellants need binders, stabilisers, and other additives that cased propellants do not. That's why the propellant weight of the 4.7mm caseless is so high relative to bullet weight.
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Old 09-28-2017, 08:40 AM   #63
DouglasCole
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Default Re: GURPS ULTRATECH ballistics?

Quote:
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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Old 10-07-2017, 09:09 AM   #64
hal
 
Join Date: Aug 2004
Location: Buffalo, New York
Default Re: GURPS ULTRATECH ballistics?

For those interested in Caseless rounds...

Do a search on Caseless rounds good bad ugly.

There will be a pdf entry listed as:

http://www.forgottenweapons.com/wp-c...Small-Arms.pdf

There, if you read the presentation, near the end of the PDF, you will find some rather eye opening "issues" that included total destruction of the weapon, along with stoppage clearing issues that were estimated at 10 minutes to clear. The 50% round weight estimate seems to be pretty much on the mark according to this - but the pictures showing what happens to cause stoppages included cracked cartridges amongst other things.

The author also mentions that the Brass case cartridge has specific benefits. I would suspect that those interested will look the document up, those not interested, will not. As for myself? It makes me more determined NOT to use caseless round weapons for my cyberpunk campaign.
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