I am not an engineer, I do my best! It turns out I was slightly wrong about the recoiling mechanism on the KRISS KARD. The barrel is fixed and does not recoil. A telescopic1 bolt carrier (for lack of a better term) is what actuates the forward recoil system.
It is a very clever design. The fixed barrel should, in theory, improve accuracy (although many non-fixed barrel gun provide excellent accuracy) and make it easier to attach suppressors and other muzzle attachments. A carbine conversion kit would be a no-brainer for this gun.
Telescopic means extends forward of the barrel. Telescopic bolts are commonly used in SMG designs because they save space and shift weight forward of the chamber. In this case the bolt and bolt carrier are separate. ↩