There are 5 kinds of guns for the Artillery units: Rifle, Shotgun, Machine Gun, Flame Gun and Frost Gun. It is strongly recommended to bring all kinds of guns in your unit arsenal. The point is, you have to bring different ammunitions before you pull the trigger.
Here is a good news for you from the Alliance.
The Ammunition Center has just reported to the headquarters that a new kind of ammunition is now available -- Universal Ammunition!

Each Universal Ammo Pack will only cost you 10 Zero Points! It will be available in the Shopping Mall next month!
Keep your eyes on the official website for more updates!