Can 'Metal Storm' Technology be used in small 100-130mm cannons used on ships?
Sure it can - but in addition to what Tim said, the RoF advantage Metal Storm has over more conventional, high-RoF guns (like Mk 45) all but disappears at that scale. Especially when you factor in any weight penalty, assuming you're just scaling up current Metal Storm models.
That's not to say that the idea of an "electric gun" is dumbfounded - in fact that's the idea behind a
railgun and
coilgun (or even better, a
multi-stage coilgun). What Metal Storm
really does is add unnecessary complication to those ideas, basically making a
Nordenfelt coil-gun.
Why? Because it's cool, probably.