DIY Bombs

[Cheomesh]

EDIT: Title was supposed to be DIY Bombs, Frags, Etc but I evidently a word or there.

So I am noticing a slight issue with the maths in GURPS for explosion calculation.

I am attempting to make my own fictional grenade/bomb/dohicky. B415 has the formula for figuring out dice from weight, or weight from dice, and a little table (that HT expands on) for explosive force multipliers for various materials.

But, the math always turns out in the same formula as a result: 6dx(some number). I run into two issues with this.

1) Lots of explosives aren't 6dx(something). How would we derive those?
2) Using that formula, an M26 grenade with 5.5oz (0.34375 pounds) of Comp B would be doing 6d (6d*1.387, really - 6dx SQRT(.34375*4*1.4), not the 8d+2 we see in High Tech.

I might be missing something. Either I've glossed over the right section somewhere, or I am not quite finishing the math - should I take the 6d*1.387 and solve it as 8.3d - which should be 8d+1? My instinct says yes, but just because it came out this close this time doesn't mean I've actually found the working answer.

Thanks!

[Varyon]

Convert the 6dxn into something workable. As you've already noted, 6dx1.387 works out to 8.322d, which is indeed 8d+1 (to determine what the +n value is, simply chop off any whole number and multiply by 3.5; remember that +3 can be written as +1d-1). For fragmenting rounds, these scale (thanks to user Ulzgoroth for pointing this out) as 1d/20mm. Creating and throwing the fragments robs the bomb of some of its kinetic energy, however - every 2d of fragmentation is -1d to the explosion's damage.

[Bruno]

Big booms (as well as big bullets and other big sources of damage) tend to get "simplified" into 6d times something on the weapon tables. That's a good number of dice to be satisfying and show off the bellcurve nicely, but not so many dice that most people don't get tired trying to add them up, and it doesn't become very heavily bellcurved. EDIT: Probably, "expected number of d6s at the table" factored in too - I forget this because I play online now with infinite dice pools, and I have scads and scads of physical d6s because I have a low Self Control Rating on my "Compulsive Dice Buyer" disadvantage.

There is no significant game difference between 6d x 3 and 18d - it's a user-interface issue.

I suspect the explosion rules don't include a note about sub-12d "dice pools" and how to sort them out because a) space and b) they expected most players to be looking for big booms BIG BOOMS.

They could have set up the formula to result in "raw" dice and then added an extra step that optionally converts to the 6dxwhatever format but I can see why they chose not to.

[Cheomesh]

Originally Posted by Varyon

Convert the 6dxn into something workable. As you've already noted, 6dx1.387 works out to 8.322d, which is indeed 8d+1 (to determine what the +n value is, simply chop off any whole number and multiply by 3.5; remember that +3 can be written as +1d-1). For fragmenting rounds, these scale (thanks to user Ulzgoroth for pointing this out) as 1d/20mm. Creating and throwing the fragments robs the bomb of some of its kinetic energy, however - every 2d of fragmentation is -1d to the explosion's damage.

Cheers; so I was on the right track in finishing the equation? At first it looked like I would be multiplying 6d by the formula result after the roll, so it would be notated as 6dx(number).

Where do the rules for Fragmentation scaling / stealing explosive energy come from? Sounds like something I'll need to remember (and cite eventually). It plays a little weird with the numbers as well, since HT gives this grenade as being 8d+2 [2d], which implies it should have been calculating out to 9d+2 originally.

M.

[Ulzgoroth]

Originally Posted by Cheomesh

Where do the rules for Fragmentation scaling / stealing explosive energy come from? Sounds like something I'll need to remember (and cite eventually). It plays a little weird with the numbers as well, since HT gives this grenade as being 8d+2 [2d], which implies it should have been calculating out to 9d+2 originally.

M.

Both are interpolation from available stats. The frag number is consistent across almost all explosives that have both a given diameter and frags. The damage reduction is derived from a particular grenade in HT which has an optional fragmentation jacket. I suspect that the reduced blast is not a consistent rule, though I couldn't tell you when to expect it and when not to.