First of all, excellent mod! I do not have the skills to make an actual mod, so this is greatly appreciated.
I agree with your balancing approach of reducing the range of the light artillery and compensating the rate of fire. IMO the original ammo does far too little damage and this ammo does a tad too much. Would be awesome if you could add a mod setting to edit the ammo damage so I can experiment from 100 to 75.
Sure, the light artillery can fire regular shells, but with its reduced range, it makes no sense to load nuclear+ shells (that's what big bertha is for).
Edit: The muzzle flashes appear to be too far in and to the left of the artillery nozzle. Minor visual bug.