Shadowrun uses Drone Mines. Nasty little buggers. When someone rides or approaches close the mine releases (if I remember) 5 mini-drones that can cause all sorts of problems - one image shows the little dragonfly drones cutting into a vehicle's tires, etc.
Your Mecha equivalent of Thunder-Aug Mines maybe?
So if you can find a delivery system that won't knock the hell out of them - like Klink's armor piercing suggestion - having little drones released inside a target would be a neat weapon.
Think about the possibilities - fire a couple of these rounds into a building filled with infantry. The drones release and run havoc, ravaging anything inside. Depending on how you've written your universe (maybe the side using this weapon have RFID tags embedded in their soldiers for identification purposes...) and there's a hostage situation. A rescue Mecha fires a couple of rounds and only the terrorists are attacked by the drones. Anyone with the RFID tag is ignored/spared.
Would certainly make boarding operations a lot easier...