[WhyKill]

Gas pressure just can't linearly accelerate something as efficiently as magnetic force can. You can get so much more velocity for the same barrel diameter instead of scaling barrel diameter and thickness because you have thrust being added through the whole length of the barrel instead of gas pressure being used to propel a slug at the end and then dissipating.

[xyzzy_plugh]

Yep, this is really a "why not both?" scenario.

Chemical propellant in first stage, electromagnetic acceleration in the second stage.

I'm curious if they want plasma projectiles explicitly, but I guess it's all kinetic at the end of the day.