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Old 02-11-2014, 08:46 PM   #1
Tyneras
 
Join Date: Oct 2007
Location: Kentucky, USA
Default GURPS Ballistics: Modifying gun damage with REF?

In my own GURPSified take on the Spelljammer D&D setting and several other kitchen sink settings, a wide variety of guns and forms of ammunition and gunpowder are available.

From serpentine to shattersand to smokepowder and more exotic variants. One thing I would like to do is figure out how substituting one explosive for another might change a gun (assume it can take the extra pressure).

Now, using some algebra on the train, I've been able to determine the proportions of shot to powder, at least in the Low Tech guns.

So, if I substitute a new powder with a different REF, how would I figure out the new damage of the bullet?
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Old 02-12-2014, 06:45 AM   #2
Captain Joy
 
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

Quote:
Originally Posted by Tyneras View Post
In my own GURPSified take on the Spelljammer D&D setting and several other kitchen sink settings, a wide variety of guns and forms of ammunition and gunpowder are available.

From serpentine to shattersand to smokepowder and more exotic variants. One thing I would like to do is figure out how substituting one explosive for another might change a gun (assume it can take the extra pressure).

Now, using some algebra on the train, I've been able to determine the proportions of shot to powder, at least in the Low Tech guns.

So, if I substitute a new powder with a different REF, how would I figure out the new damage of the bullet?
Quote:
Originally Posted by B415
An explosion doing 6dxn damage takes (nxn)/4 pounds of TNT. If you are using an explosive other than TNT, divide the weight required by its relative explosive force (REF)…
Unless I'm missing something (And I was; see below.), I would just use the RDF as a multiplier to the damage done.

Significant Edit:
Quote:
Originally Posted by B415
…to determine how much damage a given weight of explosive will do: damage is 6d x square root of (weight of explosive and lbs. x 4 x REF).
So now I think you should use the square root of REF as a multiplier to the damage done.

It could be argued that in typical demolition situations, the explosive force is not nearly as focused, such as it is in a gun's tube. So, you might yet justify simply using the REF as a straight multiplier.

Last edited by Captain Joy; 02-12-2014 at 06:52 AM. Reason: There is a bit more to the story.
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Old 02-12-2014, 08:33 AM   #3
DouglasCole
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

Most guns will be limited by their chamber pressure limit. Unless you change that, the limit on velocity won't change much.

Now, a slower burning explosive will have a big impact on velocity, due to being at max pressure longer.

If you can assume redesigned guns and big pressures, I can get an answer by plugging into my spreadsheet. Give me ten minutes.
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Old 02-12-2014, 10:18 AM   #4
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

REF won't be especially useful, because it's usually normalized for destructive force, and good propellants actually aren't especially destructive.
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Old 02-12-2014, 10:27 AM   #5
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

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Originally Posted by DouglasCole View Post
Now, a slower burning explosive will have a big impact on velocity, due to being at max pressure longer.
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REF won't be especially useful, because it's usually normalized for destructive force, and good propellants actually aren't especially destructive.
Out of curiosity, is there an inverse function or bell curve that could be implemented?
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Old 02-12-2014, 10:40 AM   #6
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

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Out of curiosity, is there an inverse function or bell curve that could be implemented?
Not really. The point is mostly that the weight of the chamber and case is largely a function of peak pressure, while muzzle energy is a function of pressure over the entire period the bullet remains in the barrel. Given the same energy content, a fast-burning explosive and a slow-burning explosive won't produce dramatically different bullet energies, it's just that the slow-burning explosive will require a significantly lighter gun.
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Old 02-12-2014, 01:33 PM   #7
Tyneras
 
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

Assume whatever arbitrary fantasy gunpowder analog is specifically a propellant. In High Tech, the expanded explosives table has propellants that go from REF 0.3 serpentine to REF 1.2 guncotton. I think that gives plenty of wiggle room.

I'm mostly looking at TL3-4 guns, which we can assume are designed to handle whatever propellant they are given. Solid orichalcum muskets, anyone?

I had just assumed pressure loss would be proportional. The same design would lose 50% of the energy as black powder or guncotton, assuming the musket is infinitely strong.

And thanks for the idea of just diving by the squareroot of the old REF and multiplying by the square root of the new REF.
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Old 02-12-2014, 02:12 PM   #8
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

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I had just assumed pressure loss would be proportional. The same design would lose 50% of the energy as black powder or guncotton, assuming the musket is infinitely strong.
That will result in ahistorically large amounts of powder, since you generally just use however much powder your barrel can handle.
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Old 02-12-2014, 02:59 PM   #9
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

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That will result in ahistorically large amounts of powder, since you generally just use however much powder your barrel can handle.
I think you misunderstand. What I mean is that is you substitute one propellant for another, pound for pound, without worrying about the barrel exploding from the more powerful propellant. I'm not saying I stuff the gun to capacity because it's indestructible.
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Old 02-12-2014, 03:05 PM   #10
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Default Re: GURPS Ballistics: Modifying gun damage with REF?

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I think you misunderstand. What I mean is that is you substitute one propellant for another, pound for pound, without worrying about the barrel exploding from the more powerful propellant. I'm not saying I stuff the gun to capacity because it's indestructible.
That's going to require some sort of magical propellant that isn't more stressful on the weapon but otherwise functions with a higher REF - which certainly isn't out of the question for dealing with things like Essential Gunpowder or whatever. That, or virtually indestructible barrels... which would logically simply result in stuffing more powder in.
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