The mini rail cannon was a powerful projectile weapon produced by Rika/Moab that was used by the droid Solis during the Clone Wars. It fired streams of superaccelerated metal that could destroy a combat droid with a single volley.
The cannon was used by Solis in the Crying Room where he liquidated six A-series assassin droids and rescued Whie Malreaux and Scout from Asajj Ventress.