For true sci-fi fans, any mention of a real-world rail gun will draw an instant, slightly audible gasp. Instead of relying on chemical propellants -- such as gunpowder -- a rail gun uses magnetic "rails" to launch a solid, nonexplosive projectile at incredible speed. Theoretically, rail guns would be able to precisely strike targets at extreme ranges, and would negate the risks associated with carrying around tons of explosive ammo. More to the point, they're cool-sounding, just like lasers.