Interesting I am trying to find out some info about this harp gun.
Anyway from here:-
250 kg projectile accelerated at 13,000 peak G's to 2,300 m/s muzzle velocity
This 2,300 m/s is the fastest muzzle velocity I can find.
Anyhow those seem like the sort of speeds at which you will have serious heat problems perhaps, maybe also that is why the stopped the project.
Furthermore it seems this is not actually a gun at all!!
It seems like it fires a rocket.
As you can see here it seems to be a gun fired rocket, which is ineligible!!
The altitude reported earlier of about 180km is wrong as it is no applicable to a gun.