Forget about random timing, use some form of fuzzy state machine with a series of heuristics to decide what to fire and when. Each weapon has a different set of attributes. Total range, damage, amount of ammunition, accuracy (at different ranges). There will always be a best answer, the laser is overheating so use the autocannon. The target''s far away use the LRR, the target''s moving fast use a fast moving weapon. Each weapon will also have a firing rate inhibiting when it can be fired and there will also be situations when the heuristics decide that no weapon should be fired due to a a lack of need or lack of an appropriate gun.

Make sense?

Mike