This is Freya's Hero Quill Gun from Aeon Flux. This is the 'functional' gun, meaning it has a motorized barrel that spins when the trigger is pulled. This gun is very heavy as it's entire body is cut from a 1/4 inch thick sheet of aluminum with resin parts glued on to it. One side of the stock can be removed (held on with magnets) to replace the two 9-volt batteries that power it.

Here's a publicity still of Freya carrying the gun:

And some screen grabs from the movie itself. In the first two shots the barrel is rotating, and CGI
quills and puffs of smoke have been added.