The US Navy's experimental electromagnetic railgun is well known by now. There's a new round for it known as the Hyper Velocity Projectile. You can read about it here, and see it being tested in the second half of the video clip below. It's guided, and zips along at 5,600 mph (or over 8,200 feet per second - almost three times as fast as a typical M16 rifle round).
Here's a photograph of the damage done to a steel plate by the Hyper Velocity Projectile (one of which is being held by the man on the left) during testing.
Makes it look a bit fragile, doesn't it?