Why? Because why the hell not!

Cluster Shells is already very powerful, my favorite in fact, but make a stronger version...
Yeah, i think its possible, a bit more range, damage, maybe some piercing to dont explode on trees, and of course, Green Explosions...

Yeah! Will be very usefull for those juggernaut Rampant biters...

ok, i didnt played the new version yet, but i just installed Rampant and some other mods and run a test.
FUCK, even with bobs equipments totally Broken, the last tier of biters and spitters are fucking hard to kill. The only effective shell was the Piercing one...
I really need to make at least one more tier of ammo and new equipments

You said somewhere that you will maybe make a 4th tier, and i think you should. Also I think you should make 3-4 tiers of ammo : crude, normal, uranium and maybe antimatter/fusion (or something).
Crude - shells, cluster shells, maybe piercing shells, rockets
Normal - shells, cluster shells, high explosive shells, piercing shells, rockets, high explosive rockets and those other rockets already in the mod, mines, heavy mines for the 3rd tier
Uranium - shells, cluster shells, atomic shells, piercing shells, rockets (I think the uranium rockets are propably the best already in the mod so no need to improve that), atomic mines for the 4th tier
Antimatter/fusion - shells, cluster shells, Tsar shell (Tsar Bomba), rockets (uranium rockets<this<atomic shells)

Also take your time and don't forget these are just suggestions not instructions on how you should do it.

Already doing, but the graphics are the hardest part for me.
For now, im planning to add more uranium ammo, and a few other types of ammo, like plasma, anti matter and dark matter. More equipments is also in line, Stack-able shields, nuclear reactor mk2, more tiers of laser and Plasma Turrets, and more.
The explosive types of ammo will destroy cliffs and all ammo will have a small push-back if the target dont die.
Also i will try to implement the Reload Scripts from Schall mods.

Sounds great!