Since modern anti-ship missiles are commonly capable of violent evasive maneuvering prior to impact, I doubt this gun can do much to them.
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Missiles are able to Maneuver quite a bit but movements take time. These projectiles travel at 1-1/2 miles per second or there-abouts, so when the missile sees it from two miles out it has about 1/2 second to decide what to do and get it done before being hit. As much mass as a missile is it can't move that fast in changing course. By the time the onboard computer gets the message to the control mechanism the slug will have already hit it.
It is simply hard for a person to conceive just how fast these rail gun slugs are.