Wandered into hree after stumbling over your images on Pintreset. (I had originally been looking for images of 'Swordguns. )
Noticed your comment about the 'Gravity cannon' aspect.
So, for a reality where they can create/simulate gravity (Every one walks around on the deck ala StarTrek/StarWars) being able to just 'Ramp up' said mechanisms to create little packets of comrpessed doom would thence not seem to be too much of a streatch.
The thing with black-holes as I understand it is not that they'd squish things on impact (Kind of) BUT that you're at risk of the 'Evaporating' (A side effect of Stephen Hawking' s theorys regarding relativiy and such) before they got to the target.
Basically there's a limit (Schwarzschild radius) that's basically the geometry between the amount of mass/gravity and it's 'Size'. Enough mass/gravity below a certain size and 'Foomp!' black hole. Not enough mass/gravity below a certain size and 'BOOOM!" all that energy is free to instantly expand again.
So... you'd kind of need some sort of automatic range finder on the gun to let the onboard computer systems know how far away the target is such that the black-hole being sent down range 'De-fooomps' at just the right time/distance.
Hope my ramblings were slightly entertaining. :D
Very much cheers to you and yours.