Many people are confused about what a rail gun is and many believe that they don't actually exsist.  In actuallity they have been in developement for over 20 years, mainly
under contract from the US government.  The rail gun gets its name from the two metal (usually copper) rails that run the length of the gun.  Current runs along these rails
and travels through a magnetic field around the armature (projectile). The reaction between this magnetic field and the current is a force that is directed down the rails of the
gun and pushes the armature out of the gun at incredible velocities.  However, producing a force large enough to accelerate the projectile to these desired velocities requires
an enormous amount current.  This limits how small the rail gun can be.  As you can see from the pictures above you probably won't see anyone (even Arnlod) running
around with one of these as a hand held  tactical weapon any time soon.  Not only would you have to have superhuman strenght to pick the gun up, the recoil from
shooting one of these would knock you on your back. (conservation of momentum)
 

  The above rail guns were all made at the University of Texas Center for Electromechanics (CEM).  To date the lightest and most tactically figured EM gun produced by
CEM is shown in the  picture on the right.  It weighs 385 lbs, has a 30mm bore and is 2.2 m long.  If you look at the first picture on the left, you can see that this
rail gun looks very much like the turret of a tank, and once the proper technology is developed could be easily integreated onto a tank.  The middle picture is a .60" caliber
rail gun with a three shot pneumatic autoloader, and is 1.6 meters long.