Hey dudes, I have a "superweapon" style gun I need to stat out properly based on its implications, and I'm looking for opinions. I found the concept of a "nuclear pulse cannon" from reading old Scifi (I think I way reading Heinlein) wherein ships carried "cannons" that were little more than mirrored "firing chambers"- the idea being, that a nuclear weapon would be detonated within this mirrored chamber and directed out a hole or barrel (similar to how radiation therapy is done, at it's core), 'firing' the nuclear blast into a jet. It's principles are also being considered for many concepts of interplanetary ships, as "nuclear pulse propulsion" is one of the few ways we know of that can propel a ship to C-fractional velocities.
The fluff is that the Rim Worlds Republic- of course- realized that the star league would royally (heh) push their shit in once terra was conquered, and the Nuclear Pulse Cannon was one of the few "wonder weapons" that was successfully created. Though it was little more than a specialized breach-loading cannon that "fired" nuclear rounds, such a weapon cannot be shot down like missiles against AMS and have some ability to fire into orbit; and since the weapon is firing a nuclear charge instead of launching one and relying on the shockwave, it could be mounted on most any vehicle and could avoid some of the harsher issues of fallout.
It's problem is that naturally it's not nearly as powerful as typical atomics, it makes the firing unit radioactive, the cannons themselves have to be readily replaced, and it's a direct-fire artillery weapon. Such a tool would also "normalize" the use of such nuclear weapons which I feel is the reason why the project was taken and hidden by a handful within the Republic who had more sense than the others (and is ironic)- and that's how its found by the players, in a bunker stashed on an airless rock along with it's attendant mech.
Rules wise, I'm gonna use Arrow IV launchers and tons of ammo as baselines but jack the heat up to 15-20 points per firing, plus 1D6 for any radiated heat from the munition. Since BT's ammo count per ton is wonky, 1 "ton" of munitions equals 3 rounds of charges, and after 20 uses the whole barrel and assembly has to be replaced- which is enormously difficult since the gun becomes radioactive due to firing.
My problem is that I don't know what I should do for damage. I was thinking Area of Affect with the blast spreading out in a cone from the struck unit, with minimum of 25 damage applied with +2D6 heat to it but only if they are a sealed unit, i.e. battlemech/aerospace fighter/dropship ecetra but DOUBLE if the unit lacks any sealing, since you know, you just got nuked in the damn face. But in a weird sense, I don't know if that's *enough* and if it doesn't hit that sweet BFG-like spot where this heavy weapon HAS to be used, but each shot still has to be shepherded and cared for, if my players decide to actually use it. Thoughts? Comments? I'm all ears, even if you hate it.