How do I make a kill npc for Exp but is for guns?

I have tried many tutorials and other methods but nothing that I find works with guns only swords. Can someone please help because I am trying to make a zombie game but I can’t if you can’t get Exp from killing a zombie with a gun. And I am not the best scripter so idk how to get this accomplished.

After the bullet touches the npc checks if the npc health is 0, If it is then, Add the exp MAYBE?