Quick sugestion.
What if one of the next guns is for a support mission? Instead of fighting directly, u give close support to ally troops in a raid.
Maybe the gun could be a Rifled 152mm Howitzer with a big splash damange but a smaller point damange and slow reload.
It could be cool.
Or maybe a 100mm with HEAT instead of APFSDS, like, better damange against mechs and armored biological enemies with higher RPM than the 120 but less damange against armored enemies (cool idea might be an Armored Crab, like the Paguroidea (Hermit Crab) when they use metal shells or the Limulidae like the Limulus Polyphemus (Horseshoe Crab) wich would be like mini-bosses that are harder to beat than normal crabs)
Interesting. A few people have suggested howitzer/mortar weapons before, but much like with the stackgun I worry it could become a bit too OP since you can fire over buildings.
I've since changed the smoothbore cannon quite a bit, so it's a lot more powerful now. Also other crab-like enemies are planned, I appreciate the suggestions.