The reason that nobody uses the railgun is that the server is running the "Excessive" mod. What this mod does is:

1. Give a player 300 health and all weapons on respawn
2. Health and ammo levels regenerate at slow rates
3. There are no ammo or health items on the maps
4. Your own weapons don't hurt you, so you can do massively high grenade/rocket jumps without sacrificing any health
5. All the weapons fire at insane rates or have increased damaging properties.

With the excessive mod, the railgun fires like a machine gun - but it doesn't do a lot of damage, and it's hard to hit your target multiple times. The machine gun on the other hand, is very useful at long range.

BTW, you don't need to do anything to your local computer to use this mod. Just connect to a server and rock n roll. just play and you'll understand....