The kinetic energy of an object is E=1/2*m*v^2 where v is the object's velocity. So if the damage calculation tracks the velocity, increasing it should increase damage too.
Also, which one is better for melee weapons, stainless or carbon steel? Is there even a significant difference?
Have you considered a nuclear reactor? At least Vault City and their ghoul neighbours and Enclave used nuclear power in Fallout 2. And I suppose if Vault City did, most if not all other vaults did as well. Broken Hills was a town that mined and exported uranium.
It should be a fairly large building and require many scavenged parts to build. It should not be something that can be constructed from the very beginning with default embark points.
Perhaps make the reaction that creates depleted uranium (U238) also create a lesser amount of "uranium fuel rods" or something similar, U235 in any case. Or make a separate reaction that takes multiple pitchblende so one has to make a decision if they want ammunition or fuel.
Now as what it might do. Perhaps it would take U235 fuel and turn it into power cells, which could be used as an alternative fuel of sorts in certain reactions. Extracting aluminium from bauxite is done with electricity for example. This could save precious coke for things that cannot be made without, such as carbon steel. Or it might just produce coke as it sort of a generic fuel in Dwarf Fortress. In any case, one pitchblende should be worth quite a bit of fuel as otherwise it would not be worth the investment.
Perhaps every time the reactor is used, it could also create a rock that boils immediately in room temperature and causes some kind of syndrome to emulate radiation. However it should be fairly easy to resist or have a minor but cumulative effect (if possible) because a properly built, maintained and operated nuclear reactor is quite safe.