Doe burned through 300 low rank mana stones each time the gun was fired. Also, it was not built to be a rapidly fired gun, so if it was fired too many times in a row in quick succession then there was a good chance that the gun would overheat.
"Luckily, I was already prepared or else the eastern region would have been decimated and that would affect everyone's bottom line. It would also create chaos in the city costing us even more to repair it and we would lose a good number of our potential labor force." Said Doe. Using the zoom feature on the screen of the gun he saw that Carter was sprinting carrying Wesley and Dorian in his arms towards his royal palace.