Okay, a bit o' good ole' thread necromancy.
The thoughts were still nibbling at me and having too little imagination, I called in the physics to my aid. What did I end up with is kinda Excel-based ballistic calculator. You put in a gun you want, set up the gun at its max range settings (45°or so elevation) and tweak ballistic coefficient until your and theroretical max range agree. Then you can play with angles.
The recults are shown in three graphs. One for "long range arty", reaching up to 80 km, and two "SP-scale" reaching to 10 km (200 hexes). You can even set up terrain of your choice there
Tried to factor in even changing air density, but the formulae are still rather "approximate", not least because not only air density changes with altitude, but also the aerodynamic coefficient changes with speed. But what the hell, it is "accurate enough" for my purposes. If you want to play a bit with it, you have it here
