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Old 06-04-2021, 09:12 AM   #1
Donny Brook
 
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Default Detonating Cord question

Det cord is listed in GURPS High-Tech on page 187. It says a pound of it would do 5Dx2 cr ex damage.

My question is, how much damage would it do when a line is laid out to a charater stepping over it?
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Old 06-04-2021, 10:03 AM   #2
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Default Re: Detonating Cord question

Well, det cord has 0.066 lbs. of explosive material (PETN) per yard, so, that's the damage for that hex.

I don't think the other two neighbouring hexes contribute much. Maybe a +1 or so to damage.
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Old 06-04-2021, 10:13 AM   #3
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Default Re: Detonating Cord question

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Originally Posted by Donny Brook View Post
Det cord is listed in GURPS High-Tech on page 187. It says a pound of it would do 5Dx2 cr ex damage.

My question is, how much damage would it do when a line is laid out to a charater stepping over it?
Not much. Detonating cord seems to top out around 50 grains per foot/10 grams per meter of explosive, with 3.6 g/m being particularly common, so if you stretch it in a line, about 0.02 lbs of it go off in your hex, for around 1d-3 damage. With the fall-off with distance anything contributed by the 0.02 lbs in the hexes to either side, let alone further away, can probably be considered pretty negligible. If you doubled it up a few times, I suppose you might be able to get a few dice out of something you could still reasonably call a line rather than a pile.

Remember this stuff isn't intended to be used to damage stuff, it's supposed to be used a *detonater* for setting off other explosives. Asking how much damage it will do is like asking how much a blasting cap will. From the designer's standpoint the "ideal" case would be zero, it would be able to set off explosives but be totally safe by itself. The manufacturers have done everything to minimize the damage, and maximize the difficulty of setting it off, that they can get away with without causing it to no longer work for the intended purpose.
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Old 06-04-2021, 10:17 AM   #4
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Default Re: Detonating Cord question

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Originally Posted by Icelander View Post
Well, det cord has 0.066 lbs. of explosive material (PETN) per yard, so, that's the damage for that hex.

I don't think the other two neighbouring hexes contribute much. Maybe a +1 or so to damage.
Doing the HT calculation I get 14.5 pts of damage (4D) for the occupied hex and 1/3rd that much for occupied hexes adjacent and 1/6 that muhc for hexes beyond those..

If anyone wonders I multiplied the actual weight (.066) x the REF (1.8 for PETN) and then took the square root and multiplied that by 42 (damage for 1 lb of TNT). I believe that's the right order for the operations.

I don't necessarily trust the formula for explosive charges so small.
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Old 06-04-2021, 10:30 AM   #5
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Default Re: Detonating Cord question

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Originally Posted by malloyd View Post
Not much. Detonating cord seems to top out around 50 grains per foot/10 grams per meter of explosive, with 3.6 g/m being particularly common, so if you stretch it in a line, about 0.02 lbs of it go off in your hex, for around 1d-3 damage. With the fall-off with distance anything contributed by the 0.02 lbs in the hexes to either side, let alone further away, can probably be considered pretty negligible. If you doubled it up a few times, I suppose you might be able to get a few dice out of something you could still reasonably call a line rather than a pile.

Remember this stuff isn't intended to be used to damage stuff, it's supposed to be used a *detonater* for setting off other explosives. Asking how much damage it will do is like asking how much a blasting cap will. From the designer's standpoint the "ideal" case would be zero, it would be able to set off explosives but be totally safe by itself. The manufacturers have done everything to minimize the damage, and maximize the difficulty of setting it off, that they can get away with without causing it to no longer work for the intended purpose.
It's not completely negligible - you can, for example, cut a small tree down with a loop of the stuff, but I agree that for game purposes if you're not in contact with it, it's going to be more nuisance than damage.
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Old 06-04-2021, 12:32 PM   #6
Donny Brook
 
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Default Re: Detonating Cord question

Hm.

Using Icelander's figure of 0.066 lbs per yard, the High-Tech REF of 1.7 for PETN, and the explosive damage formula from Basic p.415 (6x(SQRT(weight*4*REF)) I work it out to 2.34 dice or 2d+1 damage.

If it was wrapped around something it would do the max damage = 13.

Last edited by Donny Brook; 06-04-2021 at 12:36 PM.
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Old 06-04-2021, 12:50 PM   #7
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Default Re: Detonating Cord question

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Originally Posted by Donny Brook View Post
Hm.

Using Icelander's figure of 0.066 lbs per yard, the High-Tech REF of 1.7 for PETN, and the explosive damage formula from Basic p.415 (6x(SQRT(weight*4*REF)) I work it out to 2.34 dice or 2d+1 damage.

If it was wrapped around something it would do the max damage = 13.
Something in your math is wrong. I'm getting 4d using the same numbers, which is right at sqrt(3) times your result.
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Old 06-04-2021, 01:16 PM   #8
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Default Re: Detonating Cord question

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Something in your math is wrong. I'm getting 4d using the same numbers, which is right at sqrt(3) times your result.
Oh, dang. I had a percentage of bullet weight value from a prior calculation in my spreadsheet. But now I come out with 4d as well.
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Old 06-04-2021, 02:27 PM   #9
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Originally Posted by The Colonel View Post
It's not completely negligible - you can, for example, cut a small tree down with a loop of the stuff, but I agree that for game purposes if you're not in contact with it, it's going to be more nuisance than damage.
The key fact here is the fact that you loop the det cord around the tree, which has the effect of compressing and directing its explosive power. That sort of demolition is exactly what det cord is good for on its own.

Arguably, the force of very small explosions of uncompressed mostly undirected force, like det cord laid straight and loose along the ground, will taper off faster than GURPS RAW. The 4d figure calculated by others would probably be most appropriate for people very close to the explosion or even in contact (rather than x3 damage for contact explosion).

Apparently, det cord also comes in different grades, with greater or lesser REF per yard/meter, so the GM can adjust damage levels, as can someone who makes their Explosives (Demolition) skill roll.

FWIW, here is video of a length of det cord exploding:


https://www.youtube.com/watch?v=wVmWtCGyEYs
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Old 06-04-2021, 02:35 PM   #10
Donny Brook
 
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Default Re: Detonating Cord question

The use-case here is that my players want to make an impromptu bangalore with det cord and PVC. I figure the PVC has DR3 and for the guy standing over it the only exposed areas for damage are the legs, feet and groin.
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