GURPS Explosives: Custom Shrapnel and other ways to deal more damage

[MrFix]

I am very unimpressed with how many pounds of explosive you need to blow up an average man 5 yards away (35 pounds for C4), so I am wondering.

1) Does GURPS have any rules for creating custom shrapnel/payload/whatever to serve if not as main, but as additional damaging component?

2) Is there anything else that would make explosives more effective at range?

Would love answers of TL8 and lower.

[Icelander]

Explosives don't kill people. Fragments kill people.

See High-Tech p. 181-195, in particular the note about IEDs under 'Land Mines' on p. 189, the side-bars on 'Dirty Tech', 'Hand-Grenade Booby Trap' on p. 190 and 'Improvised Grenades' on p. 191.

Fragmentation material is not an additional damaging component for anti-personnel explosives. It's the payload, the explosive is just the means of getting it there.

[MrFix]

Thanks. I also checked out TS67 and it has such tidbit.

A typical pipe bomb is about 1’ long and weighs 1 lb.; its 0.5 lb. explosive filler does 6d [1d] cr ex. If wrapped with 1lb. of fragmentation material, it does 5d [2d] cr ex.

As far as I can tell, per 1.5 lbs of fragmentation material surrounding the explosives, the bomb gains 2d shrapnel and loses 1d cr ex.

35 pounds of c4 is about 85d+2
using this amazing formula, we can have 60d+2 bomb with 20d shrapnel pieces
and in total, the bomb will weigh 50 pounds.

Does 6dx10+2 [20d] cr ex makes sense for this?

[Fred Brackin]

Originally Posted by Icelander

Explosives don't kill people. Fragments kill people.

.....or collapsing buildings kill people. Explosions are like earthquakes that way.

Besides dropping walls and roofs on people, enclosed spaces do double concussion. This is sometimes hard to manage. When the Mythbusters did Operation Valkyrie Hitler's survival turned out to be totally non-fluky. The explosive charge was too small and the secret bunker had too many doors and windows.

The numbers I have in the back of my head say it takes just 5 p.s.i. to cave in a typical exterior wall but 75 p.s.i. to kill a human with concussion.

So throw shrapnel or drop buildings.. This is the "normal" way to attack people with explosives.

[Icelander]

Originally Posted by MrFix

Thanks. I also checked out TS67 and it has such tidbit.

As far as I can tell, per 1.5 lbs of fragmentation material surrounding the explosives, the bomb gains 2d shrapnel and loses 1d cr ex.

35 pounds of c4 is about 85d+2
using this amazing formula, we can have 60d+2 bomb with 20d shrapnel pieces
and in total, the bomb will weigh 50 pounds.

Does 6dx10+2 [20d] cr ex makes sense for this?

I'm not sure that this scales linearly up.

I'd compare this to what grenades, artillery shot, mines, bombs and other purpose-made explosives of the approximate size and weight we have available stats for. At some point, the fragments don't get much larger, there's just a lot more of them and they may reach further.

Note that TL8 500-lb bombs have around 6dx28 [7dx2] cr ex.

That tells me that your 50-lb bomb should have lower fragmentation damage, because there's nowhere near enough material to give numerous 20d fragments. I'd base stats on the 25-lb WWI bombs like the MK II (6dx6 [6d] cr ex]), but for doubling the weight, it would see some modest benefits in explosive power and fragmentation damage.

Depending on the precise quantity of explosive to fragmentation material, as well as whether it's home-made or made in a factory, anything from 6dx7 [7d] cr ex to 6dx9 [9d] cr ex doesn't sound unreasonable.

[MrFix]

Ran some basic math on the pipe bomb.

6d [1d] - no filling, just outer shell
5d [2d] - filling and outer shell

6d+2 - just the explosive?

It seems that the reasonable cap is that payload cannot be heavier than 30% of the explosive.

So 35 pounds of C4 can only have 10.5 pounds of shrapnel. Together, the stats of such bomb would be...

45.5 lbs, dmg 78d [14d] cr ex. or 6dx13 [7dx2] cr ex.

Does that make sense? Seems to roughly compare to Icelander's numbers.

[Icelander]

Originally Posted by MrFix

It seems that the reasonable cap is that payload cannot be heavier than 30% of the explosive.

Bigger bombs don't scale linearly.

Originally Posted by MrFix

So 35 pounds of C4 can only have 10.5 pounds of shrapnel. Together, the stats of such bomb would be...

45.5 lbs, dmg 78d [14d] cr ex. or 6dx13 [7dx2] cr ex.

Does that make sense? Seems to roughly compare to Icelander's numbers.

If you could get 7dx2 fragmentation from less than 50-lb bombs made in a basement, why would the enormous military-industrial complex bother to manufacture carefully machined 500-lb bombs that only match it?

If you look at the bombs on p. 194 of GURPS High-Tech, you can see that fragmentation damage rises fairly slowly with increasing bomb size. You can also look up the exact weight of explosive in each of these real-life bombs, if you want, and probably find schematics of the metal casing of the older ones.

[MrFix]

I am trying to do that, but it's very troublesome to find the "MKII US 111mm" for some reason.

Based on PUW12.5's damage die, only 2.25 lbs out of 25 lbs contain TNT, the rest being... something else. I am having trouble gathering any useful information from this, because certainly a satchel charge I'd use would have at least four times the explosive content, in REF1.4 explosive. 22.75 lbs of outer casing has no business creating only 4d+2 shrapnel.

If we assume that MKII is TNT too, then based on damage die, out of 25 lbs of a bomb, only 9 are explosive, with 16 being shrapnel that's 6d.

A very confusing situation.

[Icelander]

Note that the earliest PuW bombs were not mature technology, so it's better to use the later bombs of similar weight, when the kinks had been ironed out and the casing actually fragmented more effectively.

As explosive damage goes up, the fragments are going further and you are effectively creating orders of magnitude more 'attacks' of fragments. So you need a lot more casing material to get 6d fragmentation out to 30 yards than you need to get it within 15 yards.

This is why the required weight for the casing goes up a lot faster than the fragmentation damage.

In any case, you know that your 50-lb bomb is going to do less damage than the 100-lb GP AN-M30, which is 6dx15 [5dx2] cr ex. Based on that, I'd doubt any design that gave more than [9d] fragments at 50-lb or less and, frankly, be more likely to use, at the very most, [7d] or [8d] unless it was made by a team of engineers and technicians with access to a factory.

[MrFix]

Originally Posted by Icelander

As explosive damage goes up, the fragments are going further and you are effectively creating orders of magnitude more 'attacks' of fragments. So you need a lot more casing material to get 6d fragmentation out to 30 yards than you need to get it within 15 yards.

This is why the required weight for the casing goes up a lot faster than the fragmentation damage.

In any case, you know that your 50-lb bomb is going to do less damage than the 100-lb GP AN-M30, which is 6dx15 [5dx2] cr ex. Based on that, I'd doubt any design that gave more than [9d] fragments at 50-lb or less and, frankly, be more likely to use, at the very most, [7d] or [8d] unless it was made by a team of engineers and technicians with access to a factory.

I suppose, I just need to figure out the weight and how much explosive/shrapnel material I have to acquire for a game where I'd play a demo expert. I doubt a GM would permit me a 6dx8 satchel charge with [7d] fragments just for the price of explosive and weight of explosives (11.4 lbs)