When I was younger the military was experimenting with rail gun tech for use in space against satellites (or anything in the vacuum of space that was a target) & they had a brilliant write up about the challenges the weapon would have to overcome to be effective in the atmosphere. I wish I could recall the source for the article, I want to say it was in Naval proceedings magazine, but I read that often & it may be stuck in my memory as the source when it wasn't.
An electromagnetic gun firing a metal puck is neato & all, but I'm not sure what function it's going to serve that would make it worth more than experimentation. It would be a basis for some future weapon systems when nano-technology catches up I would imagine. A backpack on a soldier full of projectiles, no cases or firing charge to take up space, just the projectiles themselves & a near unlimited rate of fire would be the target destination if I were in charge; good thing I'm not or I'd use unobtainium for everything & the military would end up with nothing probably lol