Forget "pew pew pew," the boomsticks are here

[Ithuriel]

Also, it might not be a bad idea to try to minimize or eliminate rail-projectile contact. You can coat most of the projectile in something like Teflon and achieve electrical contact between the rails and projectile with a deliberate electrical arc. (In a vacuum, inject some gas.)

Nah. You'll reduce some of the wear, but you've still got what basically amounts to a plasma explosion inside the barrel of your gun, and there aren't many materials that will stand up to that.

I wonder if it would be possible to build the rails out of a dense, cold plasma. If it were, not only would you eliminate rail wear, but at the point at which you charge up your rails your gun barrel will emit an ominous glow. Totally worth it.

In the worst case, you might try sacrificial rails. After every few rail shots, eject the rails and slide in some new ones.

I believe that is exactly what the naval railguns will do. It'll still be cheaper than a bunch of cruise missiles or antiship missiles.

Coil guns largely avoid this wear problem, but coil guns seem to be limited to 1-3km/s velocities. Railguns aren't nearly so constrained in their muzzle velocities.

Railguns give you better bang for their size. Coilgun-based surface-to-orbit launch systems have had workable designs since the late 70s, but they're huge... lengths measure in kilometres (up to 100s of km for delicate cargo like people).

A coilgun equivalent to the US navy design in terms of projectile speed and mass (using some very quick and dirty figures, courtesy of Project Rho and Luke Campbell) would need a barrel longer than 100m, even if it were using a load of very fancy superconductors, and you'd still have to work hard to stop waste heat from destroying the projectile before it left the barrel.