Remember around this time last year when the US Navy started testing railguns as ship-mounted weapons? BAE Systems has developed an even more powerful magnetic linear accelerator weapon for testing called the 32-MJ LRG (which stands for "32-megajoule Laboratory Rail Gun" - I guess the person in charge of naming experimental weapons was hired by the federal government to name the PATRIOT Act). The experimental weapon is about the size of an airport x-ray machine, and probably masses about as much. It doesn't fire explosive rounds but then again it doesn't have to. If you can throw a projectile at eight times the speed of sound with any accuracy, chances are whatever it hits won't exist for very much longer. Even if you just barely miss the shockwave from the round passing by is probably going to do some major damage on its own.
The Navy says that it won't stop until it can deploy and fire a railgun that requires 6 million amperes of electricty to fire. That's way more power than most generators can crank out today, which is why that beast of a gun is scheduled for development thirteen years from now.
There's another problem that they're hoping will be solved before then, also: Developing materials that won't catastrophically fail the first time the railgun is fired due to the structural stress.