High Velocity

DEFENCETECH has a report, "Killer Drone Builder General Atomics Builds Killer Electromagnetic Rail Cannon", by Greg Grant, that is worthy of your attention, with a, pardon the expression, killer video that shows what this piece of ordnance, built by General Atomics, who make the Predator, can do. 

The company has been working for a number of years with the Office of Naval Research on a 200 nautical mile gun system. In a parallel effort, they’ve been developing a smaller, pulse-power technology demonstrator, called the “Blitzer,” for ship defense against anti-ship cruise missiles and small boat swarms.

It's a "short-range" weapon, with just an 80-mile/140 km reach. The projectile exits the "muzzle" at over 10,000 feet per second, or just over 3 km/sec. That's quick. Apparently, the railgun will be capable of 1 round per second, if they can supply enough electrical power, which should not be difficult for Nimitz and Aegis-class vessels. Might be just the thing for dealing with those Iranian Silkworms, as it takes a round less than 7 seconds to reach out to the horizon.

The only other gun that matched this range was "The Paris Gun", from WW1, which took all day to fire 20 rounds.