p119:
A weapon with the Storm Quality doubles the amount of hits inflicted on the target.
A normal hand-weapon firing a normal shot would have a maximum of one hit possible - ie it is Str 1.
Firing on Semi 3 it would have a maximum of three hits possible - ie it is Str 3.
If it has the Storm quality it will do up to two and six hits respectively, despite remaining at S/3/-.
This is identical to voidship components.
However, if you're going to adopt the "fire twice" rule this point is moot