Hey there, I was playing PVP the other day and one of my FED Allies was using some kind of cannon (I think it wasa cannon) that fired with a blueish translucent comet/railgun looking fx, thought it was really cool. But he never told me what kind of weapon it was, so I've been looking for one in the exchange but have no idea what it is called, and none of the ones I have seen since look like it. Any help at all in identifying this weapon type, is greatly appreciated!

It is not a weapon, it's a Science ability called Feedback Pulse.

When you activate it, any time another ship shoots you with an energy weapon you will fire back one of those blue pulses. They impact directly against hull (i.e. shields have no effect) and do damage proportional to the power of the energy weapon that was fired.

Most players who don't PvP first encounter this ability when they fight a Galor (Cardassian Science Vessel).

The only time I encountered FBP in PvE so far, it hit my shields, not my hull.

This is incorrect. FBP hits hull when used by both players and NPCs. You probably mistook the normal weapons fire for the FBP damage.

Your combat log will tell you what happened.