h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

No, no... A Gauss Rifle is more like a linear induction motor, or rather a series of them. A Rail Gun is more of a "Jacobs Ladder" device.

A rail gun is made up of two parallel rails (hence the name), with a high-voltage charge running into them. The projectile is encased in a conductive sabot, thus completing the circuit (a sabot is any bit that encases a projectile which is discarded at some point before impact, usually by air drag immediately after exiting the muzzle, and is usually used to have a positive seal against a smooth barrel, in the case of conventional firearms firing fin-stabilized projectiles). When a current is applied, the sabot is forced out of the business end, taking the projectile with it. As you can see, it is impossible to provide rotation to the projectile, so it must be fin-stabilized.

A Gauss Rifle is a series of conductive rings which are energized in sequence to pull a projectile made of a magnetic material. In the case of a ferromagnetic or paramagnetic projectile, the first ring is energized to pull the projectile, then turned off as the next ring is turning on, all the way to the muzzle in rapid sequence. The projectile may be a discarding sabot type and fin stabilized, or there may be a non-magnetic barrel with rifling (spiral grooves cut on the inside of a barrel to impart spin on a projectile- the lines you see when you look through the gun at the beginning of a James Bond movie, right before he shoots the screen) inside of the coil setup, hence the name "Gauss RIFLE". Gauss was the engineer who came up with the idea.