The DREAD
 

http://www.military.com/soldiertech/...ESRC=army-a.nl

By David Crane
Editor, DefenseReview.com

Imagine a gun with no recoil, no sound, no heat, no gunpowder, no visible firing signature (muzzle flash), and no stoppages or jams of any kind. Now imagine that this gun could fire .308 caliber and .50 caliber metal projectiles accurately at up to 8,000 fps (feet-per-second), featured an infinitely variable/programmable cyclic rate-of-fire (as high as 120,000 rounds-per-minute), and were capable of laying down a 360-degree field of fire. What if you could mount this weapon on any military Humvee (HMMWV), any helicopter/gunship, any armored personnel carrier (APC), and any other vehicle for which the technology were applicable?

This weapon sounds like it uses electromagnetics for spinning propulsion. This is more commonly used in modern trains, making them incapable of using normal railway. Search google for maglev to find out more.

Fits the brief description at least...

Leader Propulsion Systems (LPS) just informed DefRev that it has signed up with a large U.S. "defense entity" (i.e., a large U.S. defense contractor) to fully develop the DREAD technology for both lethal and less-lethal applications. This strategic partnership will also enable Leader to begin developing a family of gas-operated lightweight weapons chambered in .50 BMG (12.7x99mm), .338 Lapua, .300 Winchester Magnum and 7.62x51mm Nato (.308 Win.). (http://www.military.com/soldiertech/...ESRC=army-a.nl)
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Sounds very expensive...
I wonder when people will get a chance to see it in action?

OK, so a crew served railgun.... and what kind of battery is going to power this contraption? :munchin

that's YOUR homework assignment...