Just had a few ideas:
"rifles are not a suitable countermeasure against drones" - well this rifle might be, because the drones cannot afford heavy shielding against an EMP.
But there may be better ways to create an EMP.
Also regarding the EMP: The rifle as it is now has a plastic casing. It shouldn't be too difficult to cover it with with a metal casing designed for shielding off the EMP. It just adds weight to the whole thing.
About keeping it stealthy: Usual guns work by having an internal explosion which causes pressure against the projectile which is then accelerated. Air guns don't have that explosion,
this gun doesn't have it, so as long as you keep the projectile speed under mach 1 (so that the projectile doesn't create a sonic boom by itself), you can have a high speed without (much of) a sound, I don't know where the "tclak" sound comes from but it's low-noise.
There is something else: While air guns don't have explosions, they have a "single point of acceleration" in common with usual guns. This single "bang" drives the projectile forward through the barrel, working against the mass of the projectile until the barrel ends, the driving force is "set free" and the acceleration ends. But this rifle accelerates the projectile in stages, a little bit more at each coil. Which means that the acceleration caused by a single stage=coil can be and probably is much lower than the single "bang" of an air gun and a usual gun. This could be used to limit the acceleration force to some maximum value, say 10 G, but, say, 10 times instead of one time - and now you could shoot cartridges containing a drone that can't take more than 10 G of force.
Just some thoughts while I'm sick in bed. (Just a bad cold.)