its always handy to have a text object show the total objects, = set text to system totalobjects, now when you shoot the objects the objectcounts is raising fast...
i think the problem is that you use the spawn explosion, use the system create explosion and dont forget to destroy the explosion when alpha=0 or end of animation.
also the ticks, you have a variable that when = 1,2,3 create objects,
you should put a system trigger once condition with it otherwise it will continue to create objects when = to that number