Yugoslav 20x110 HS

I have this Yugoslavian 20x110 HS by Sloboda in 1975.
What does the TK and BK stand for?
What type of fired projectile? Possibly a practice. The previous owner grooved the case so deeply it has almost severed the neck off so I cannot see if it has a tracer.

Ron, I doubt the projectile belongs to the case as this shape/design is unknown from Yugoslavia.
Also it should have respective markings which seem not to be applied.
Is the “T D” all markings visible?

TK: technical inspection
VK: military inspection
Basically these two QA and acceptance.

Yes it has TD +. as the only markings. It came from the Slovac area? imported by a dealer. The projectile type was unknown by me so I asked for help.
Thanks for the Info so far. Ron.