Coilguns have physical limitations that make them unsuitable for extremely high velocity applications. Specifically, the engineering difficulty in switching the

Coilguns have physical limitations that make them unsuitable for extremely high velocity applications. Specifically, the engineering difficulty in switching the coils on and off scales with the square of the currents used in a coilgun. Any inductor has a rate of change of current proportional to the voltage across the ends. So all else equal, if you double the current, you double the switch-on and switch-off times. But, since you're using higher energies, you're getting a faster projectile - which means you now need to switch the coil off faster as well, to prevent suck-back. So in short, coilguns get significantly harder to build at higher energies. In contrast, railguns get more energy efficient as projectile velocity increases.