This article deals with Rail Gun as it relates to NationStates. For more general information, see the Wikipedia article on this subject.
A Rail Gun can be two types of weapon in NS:
A Railroad Gun, such as the large bore artillery favored by many armies in the nineteenth and early twentieth centuries.
A ballistic weapon that uses two parallel magnetic rails to fling a magnetic projectile, instead of a conventional charge.
This Topic Deals with the Latter Weapon
In a rail gun, the term "rail" is the common name for the projectile, although somewhat incorrectly. In firing, a powerful electric charge is flung up the first firing rail, then back down the second, arcing over the projectile rail. As the magnetic field is completed, the projectile is flung free at incredibly high speeds, exceeding eight thousand feet per second in Kaukolastani 6cm Naval Rail Guns and approaching ten thousand feet per second for Knootian 30.48cm Naval Rail Guns. Do to the longer acceleration, as well as the lack of a secondary recoil (Release of powder, as in conventional arms), the recoil is actually significantly less than a slower and heavier conventional round.
The heat created at launch is often excessive, and the projectile is partially converted to plasma. Upon impact, the kinetic energy delivered can devastate a much larger area than the rail's own impact, and the plasma wash can vaporize soft targets. As an added bonus, if the impact velocity exceeds 4000fps, the hydrodynamic shockwave will exceed the capacity of the human body to retain it, and the impact will send enemy soldiers into gooey piles. Then the plasma wash will hit.
However, the extreme conditions upon launch mean that the rail gun will have to possess sufficient cooling, slowing refire rate. The weapon also requires significant power, and a Superconductor Tech-Base will probably be required. Because of the size, heat, and power requirements, Rail Guns will probably debut as a Naval Weapon, Tank or Artillery Weapon, and then, finally, as an Aircraft and Infantry weapon. Rail gun support weapons should be feasable at the high end of Postmodern Tech or the beginning of Near-Future Tech, but standardized Assault rail guns are purely Future Tech.
Please, do not confuse a Rail Gun with a Coil Gun.