GURPS Demolitions: Custom Shrapnel

 GURPS Demolitions: Custom Shrapnel

Explosives are fun. Adventurers are always able to find things to blow up, such as Cthulhu spawn or a werewolf or a nazi tank. Except, in GURPS, the concussive force of the explosion runs out of steam very quickly. Man-portable charges are rarely lethal at 5 yards, let alone 10, so a person may feel discouraged when a big boom doesn't really kill anyone.

How is the issue resolved IRL? Well, one solid way to increase your explosive's lethality is to encase it into shrapnel-creating object. That's how a hand grenade is made - fragmenting shell and an explosive charge.

GURPS does not readily have rules for custom shrapnel explosives, but with the help of Kromm's post and Kalos's math affinity, there is now a way to create custom shrapnel for your satchel charge.

1) Take your explosives and figure out it's damage using rules on B414.

2) Gather shrapneling material.

3) Roll Explosives (Demolitions) to assemble the device. Success by 0 yields a device with up to 1:1 ratio of shrapnel and explosives. For example, 1 lb of C4 can have up to 1 lb of shrapnel, for total of 2 lb. This is equivalent to a pipe bomb in box on TS67.

For every success after 0th, you can decrease the amount of explosive needed by 5%, or increase amount of shrapnel by 5%. Maximum ratio is 19:1, with only 5% of the device being explosives. This is equivalent to factory made aircraft bombs!

4) Calculate shrapnel damage using this formula: 

x^1/3*2.35, result in dice

x=shrapnel material weight in lbs

5) Record the device's statblock: It's explosive damage, it's shrapnel damage and weight of the device.

Example:

A Werewolf Hunter wants a handmade explosive that launches silver shrapnel but doesn't explode too hard.

He takes 1 lbs of Liquid Explosive Foam (REF 1.1) and prepares a smithy to forge silver casing.

He rolls Demoliton (Explosives) and succeeds by 9, creating a very-well designed device with explosive content of only 5%.

If he wants to, he can create a 2 lbs portable satchel, with 0.1 explosive and 1.9 shrapnel material.

1.9^1/3*2=2.47 or 2d+2, see box on HT166

End result: Dmg 4d [2d+2] cr ex, Wt. 2 lbs

If he wants to, he can encase 1 lbs of explosives in 19 lbs of shrapnel, retaining the 19:1 ratio.

19^1/3*2=5.33 or 5d+1

End result: 26d+1 [5d+1] cr ex, or 6dx4+8 [5d+1] cr ex, Wt. 20 lbs.

Optional rule: Involving explosive's REF

If you have noticed, shrapnel damage has no relation to how much damage the explosive outputs, or it's REF. Folks in the thread that the Krommpost is from insist that it is realistic.

If you believe otherwise, feel free to divide the final weight of explosive filler by it's REF. Assume everything above was said about REF 1 explosive.

For example, you assemble a device that is 1 lb shrapnel and 1 lb REF 1 explosives for a total of 2 lb. If you use REF 1.4 plastic explosive instead, you only need 0.7 lbs of it to achieve the same result as 1 lb REF 1 charge. The device's final weight is 1.7 lbs when using plastique. One must be careful with this optional rule, as it allows miniscule amounts of explosive (like REF 5 Fuel-Air mixture) propel teeth-shattering amount of shrapnel. Alternatively, an unskilled person can make more effective bombs if they just use a higher REF explosive.

Notice, the damage from the explosion is STILL related to the weight of explosive. Using less explosives means the explosive damage is reduced as well. This only allows you to further reduce explosive to shrapnel ratio.