Well first off the on shoot trigger would have to be directly related to ammunition, so every turret that used it would be subtracting something every time its triggered.
Ok thats great we got that part... blah, blah, blah, but what exactly are they shooting?
That kind of limits the trigger to the object being created.
Suppose I wanted to have an additional condition like:
On tank shoot
helicoptersprite is in range
create object misslesprite
Then if your going to have a rate of fire, wont that variable have be tied to the amount of ammunition?
So now I would be stuck firing x amount of bullets, as well as missles etc.
Would it not be just as simple to create a private variable, for something that would be somewhat obscure?