All from a device with no moving parts. Computer controlled by our evil robot overlords.
"The distinguishing features of this technology are the absence of ammunition feed and casing ejection systems (the only moving parts are the projectiles), and the electronic ignition of the propellant charges.
The relatively simple external shape of the Metal Storm barrel allows for the clustering of Metal Storm barrels into a barrel array or 'pod', or for their attachment (as single units) 'bolted on' to existing weapons mounts, including infantry weapons. The absence of a mechanical feed mechanism and the inherently compact lightweight nature of Metal Storm systems also makes them suitable for attachment to light robotic ground and aerial vehicles. The electronic ignition allows for the firing of the stacked ammunitions at 'electronic speed' without any delays caused by mechanical ammunition feed mechanisms.
The clustered barrel array has been further developed with the design and building of prototypes of electronic firing control systems, allowing selective firing from any barrel in a cluster, and within each barrel the ability to control the rate of fire. This allows for responses which range from the equivalent of a volley gun discharge (all projectiles 'at once') to using (selectively) individual munitions with increasingly serious (but non-lethal) effects and lethal munitions including high explosive and air burst shells (all from different barrels in the array)."
--Otherwise known as a Big Can of Whoop Ass.