So, I absolutely love the concept of the artillery cannon, but unfortunately after playing with it and trying hard to make it work I have to say that it really feels horrible to use. I know the mod is old, but it feels like such a wasted opportunity as all the sprites/code are already there, it's just a balance problem.

Problems:

• When used on your own map, artillery works as an inaccurate but cheaper mortar equivalent which doesn't need a barrel. This works, but I'm pretty sure most people would have liked to see it the other way around: thematically, artillery should be more powerful than mortars, ie. more expensive but more accurate or with a larger blast radius.
  
• The main appeal is, of course the bombardment - unfortunately, this mechanic is completely useless as is, because it turns out, the inaccuracy makes it way too unlikely to hit anything even when firing dozens of shells. Sparing the math, but even if there are ~25 enemy pawns on the map, you only have a 1 chance out of 100 to hit them - extremely rare. Of course the artillery should be inaccurate at long-range, but it is way too extreme currently.

• Artillery accuracy radius changed to 7 tiles (vs. 8 for mortar)
  
• Cost increased to 2 reinforced barrel, 50 plasteel, but does not require barrel changes like mortar.
  
• Weight increased to 250 kg (from 30).

That's it, artillery is now a late-game mortar, more powerful than mortar and does not require barrel replacements, but a lot more expensive. It can't be transported like mortar, so you actually have a reason to use bombardments (also nice added synergy with the vanilla expanded trucks which can be used to transport it).

• Map bombardment: shells should land closer to cells where enemy pawns are located, and avoid cells where your pawns are located. It should still feel unlikely to hit but not as ridiculously unlikely as it is now. The way I suggest to implement it: pick 5 random enemy pawn, pick a random cell in a radius of 20 around its position, explode the shell there. (discard and reroll if this lands near an allied pawn).

And now admire the new artillery piece in action (I've implemented it!)

https://www.youtube.com/watch?v=4bVfVDehwn4