That's a coilgun. A railgun is basically two parallel conductive rods into which a conductive projectile is inserted while a very strong current is run through the rods, creating a very strong and very simple magnetic propulsion system that has the down side of creating a lot of friction and heat which oxidizes the surface of the rods making them less conductive if the current is strong enough to get appreciable velocities out of it.

So far it seems that's been an intractable problem: you fundamentally cannot get a useful railgun that doesn't foul its own barrel to the point of uselessness within just one or two shots. AFAIK small railguns roughly comparable to firearms don't have this same problem, but they do have the problem that firearms do what they do better in a smaller package that's more durable and time-tested.

The reason large scale railguns have been a topic of interest is because they theoretically could exceed the practical upper limit for artillery in terms of range and kinetic energy, in a package similar in size to extant naval artillery, with the obvious downsides that they experience ridiculous wear and tear and would need to replace large parts of their barrels after every single use and that modern rockets more or less render their whole purpose obsolete since even the most optimistic railgun gets beaten on range, payload, accuracy, and possible firing platform by missiles.

Edit: also IIRC the Navy railgun project was a hybrid system, propelling the projectile into the railgun assembly with an explosive charge, which could only make the fouling problem worse.

Strong electromagnets need a lot of power, and lots of power means lots of heat from conductor resistance and from the fields themselves exerting energy. Same reason why you can't clock one CPU core really high: more watts, more heat, and then shit breaks.