Replicators use a base of neutral material that the system finds easy to use for turning into other stuff. For this kind of specialized application you might use materials close to the end result lowering the energy usage to extend the life of the unit. In DS9 they had self replicating mines that were networked so that the surrounding mines would replicate a detonated mine using the material of the detonated mine.

The real problem is shields. A slugthrower would be completely negated by a personal shield. Against a beam weapon it depends on how much energy it can absorb per second vs. what the beam can shoot.