In Mass Effect 2, the following scene plays out:
This is one of the examples of well-done background dialogue in the Mass Effect series that reminds me how incredible it was to play. Paying attention to the dialogue, the sergeant cites the energy of the projectile as roughly 3 times that of Fat Man, the Hiroshima nuclear bomb. Crunching the numbers, one can see that this is not quite right:
Also, rail gun projectiles wouldn't really be visible to the naked eye, but the stuff surrounding them ought to be. Rail guns tested by the US Navy fire unpropelled, kinetic projectiles that look like this:
Yep, epic fail.