DREAD

Some guy has invented a gun that fires ball-bearings at about 1000 fps. But here's the kicker:

"Due to its extraordinary high rate of fire capability, it delivers its bullets 8.5 millimetres apart, thereby delivering more mass to the target than any other weapon."

From the description in the patent, I can't see it having any really practical application as an infantry weapon. The requirement to spin up the disc prior to firing, not to mention the inevitable noise it would make, would reduce its tactical usefulness to virtually nil--although it might find a niche use as a crew-served perimeter defense weapon.

As a vehicle-based system, however, it would make a great basis for a point defense weapon against missiles. It could be mounted on the top of a tank and slaved to a small, phased-array radar, powered by a tank's own electrical system. Additionally, it could theoretically achieve much higher velocities if the disc were of sufficient size, and ammunition capacity wouldn't be a problem as with a foot-mobile weapon. It would also double as a very effective anti-personnel weapon in close quarters--for those idiots who are suicidal enough to actually approach a main battle tank on foot.