New Weapon — Light Gas Cannon

[nick87720z]

I don't know, is hyper-velocity cannon is supposed to include this tech...
It is existing thing, used almost in research rather, than in real weapons. Combustion gas accelerates piston, compressing some much lighter gas. It has much higher speed limit, than usual powder gun.

In tech tree it could be available between currently available cannons and railguns. Also could be multi-stage gas acceleration tech, opening mentioned gun type and optionally improving existing weapons by using special ammo.