Maybe a balance thing. But the default light art. ammo is way to low damage to use. If you hit a biter nest with a few artillerys it heals faster then you can damage it.
Maybe use grenades and unlock it with mil tech that way instead of a water barrel change it to 2-5 grenades? That is also more "logical" as you are just shooting grenades through the artillery then. And then later upgrade to true big bore artillery when you get yellow science.
(Or make a mid-tier shell using grenades for more damage?)
