Wednesday, December 4, 2024

Upscaling d20 bullet damage

In a previous post tied bullet damage to the diameter of a round multiplied by the ratio of length to caliber in millimeters. This works fine for bullets which rarely go over 1 inch in diameter, and rarely have a ratio greater than 10:1 (which would max out at 10d12). I randomly mentioned this blog, and that got me pondering how the math would work out. Having looked into NATO Fox Calls for fighter planes, I came to realize that a large amount of weapon specs are available for US Munitions on wikipedia. I'm sure missiles are a bit more complicated than what is presented here, but I thought it would be worth the thought exercise. That being said, one note to mention is that in the previous post, the maximum size was d12 for 1". Most missiles are going to be more than one inch, and the inches should probably be multiplied separately from the ratio, but it seems easier to add the inches to the length ratio and multiply by that number. Both methods are shown here so anyone who wants to use them can use either method

Missile                     Dimensions (ratio) Damage
AIM-7 Sparrow (Fox-1)       ~8x144" (~x18)     d12x26 or d12x144
AIM-9 Sidewinder (Fox-2)    ~5x119" (~x24)     d12x29 or d12x120
AIM-120 AMRAAM (Fox-3)      ~7x144" (~x21)     d12x27 or d12x147
AIM-54 Phoenix (Fox-3)      ~15x154" (~x10)    d12x25 or d12x150
AGM-114 Hellfire (Fox-2)    ~7x64" (~x9)       d12x16 or d12x63
RPG-7 Round (~75x950mm*)    ~3x37" (~x13)      d12x16 or d12x39
AT-4 Round (~84x245mm*)     ~3x9" (~x3)        d12x6  or d12x9
Minuteman ICBM (~5.5x60 ft) ~5x60' (x11)       d12x785 or d12x46,800

Percentile Damage
You may have noticed that multiplying caliber and length separately produces damage in excess of 100 in all cases. It may be helpful to roll fewer dice and get bigger damage values. In that case, round the maximum damage to 100 points in whichever direction makes the most sense, and use that number of d100s. The following is the result of that.

Missile                     Damage Maximums    Percentile Roll
AIM-7 Sparrow (Fox-1)       1728               18d%
AIM-9 Sidewinder (Fox-2)    1440               14d% 
AIM-120 AMRAAM (Fox-3)      1764               18d%
AIM-54 Phoenix (Fox-3)      1800               18d%
AGM-114 Hellfire (Fox-2)    756                8d%
RPG-7 Round (~75x950mm*)    468                4d%
AT-4 Round (~84x245mm*)     108                1d%
Minuteman ICBM (~5.5x60 ft) 561,600            d%x5616**

* These may not be an accurate length, as the dimensions of the RPG-7 depend on the round, and the AT-4 is based on the previous Carl Gustav Recoilless Rifle. In any case, they're useful approximations for gaming.
** Using the lesser value produces 94d% on the off chance you wanted to make nuclear strikes survivable.

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