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OOC: Heh, supposing the weapon doubles in size for each size category, that will be from medium to collossal, so it will end 16 times the size and 4096 times the weight of a normal bomb. The damage progression would be: 4d6>4d8>8d6>8d8>16d6, reflex DC 18 for half damage. And the area would be something around 20ft, possibly +5ft or +10ft per size, to at least a good 40 ft radius. Using the explosive rules of d20 modern for this one would be pretty much overkill, with aditional (double amount) explosives increasing the damage or the area of effect in 50%. So, keeping things simple. Of course, hauling something with more than 2000 kg is a little troublesome, so siege weapons to the task.