I dont like the multiple array version of the fire comand. It makes units fire in the air (big glitch) and even when i use dowatch and dotarget it doesn't seem to work.
If i were u stick to _unit fire "weapon name"
P.S. if you want to find out other weapon names, look at the official COMREF. For addons, most addon makers will supply documentation where u can find the weapon names.
On the other hand look in the editors depot for event handler tutorials, these could help you as well especially the 'fired' one.