[mnehring]

We could reduce the diameter to six inches and still get you a muzzle velocity of 1,000 ft/sec if you were willing to carry around a rotating steel or titanium disk that was spinning at 40,000 rpm. You'd have to carry around a motor, too. :-)

Why are we assuming this is a motor driven or as others suggested a flywheel? Couldn't this be done through a controlled magnetic field, thus no need for moving parts?

[LibWhacker]

You mean like a railgun? It's true; railguns have awesome potential. Especially a nice little portable model I could slip in my pocket. But I think this particular invention involves centripetal forces; i.e., a spinning disk of some kind.