Dread isn't a railgun -- it's a centrifugal system. And it has some real problems from a weaponization standpoint, but it looks good on paper to the uninformed. The projectiles are not powered, so they exit the rotating disk with only the velocity of the outer edge of the disk, which makes supersonic projectiles highly unlikely given the forces involved across the disk if the outer edge were to be supersonic and the center subsonic. It would tear itself apart.
It can throw a lot of projectiles really fast at high subsonic speeds, but they're using sphereical projecticles, which are fairly useless to get actual range -- sort of like having a pistol that fires a lot of rounds really fast, but with pistol lethality and pistol ranges, at a weight of several hundred pounds. I'm glad these guys haven't come pounding on my door yet trying to sell us the system (the Metal Sotrm guys have, and their system, while still far-fetched, has actual potential).
Railguns, OTOH, if you can ever solve the power source problems, actually have real potential.