Rather than relying on a explosion to fire a projectile, the technology uses an electomagnetic current to accelerate a non-explosive bullet at several times the speed of sound. The conductive projectile zips along a set of electrically charged parallel rails and out of the barrel at speeds up to Mach 7.
I have always thought this was a pretty cool concept, even since when I started learning about them playing Mechwarrior games. Yeah, I used to be nerdy.

I just can't wait until they get it down to a size that doesn't need a boat to power it, and that I can fit on my belt.