In fact, it is just Math. It is complicated, you would need some Spreadsheet/Calculator but its certainly doable.
If the Mortar ammunition is the Vanilla one and not modded, I think you could find some online.
I understand your point, but I think you misunderstood me. I agree that a GMG is easier to use, and I also agree that it is much stronger.
My point is, that with this thing you would have 0% risk if you place it inside your Base. The fact that you sit open on the back is irrelevant in this scenario.
A GMG must at least show its turret to be able to fire, so you can theoretically take it out.
And this would make the Vehicle pretty much useless because you can shoot a .50 at that range effectively, simpler and much cheaper.
Don't get me wrong, I freaking love big guns, but I just do not think Artillery would fit in Exile.