The LVKV 42 uses the Lvakan M/48 (Luftvärnsautomatkanon, also the indicator for the vehicle itself, LVKV.)
This is based on the Bofors L/60, similar to upgrades for the Bofors 40/70 (otherwise called L/70, iirc)
All bofors variants keep similar structures, ejecting the shell out of the back into what i call the “Cartridge carousel.” The cartridge carousel consists of 2 structures, halfcircles facing the front of the gun structure, in a halfcircle to the floor or base of the gun structure, leading the spent casing to eject to the front of the cannon.
Since you can’t move the entire “carousel” along with the gun, only a part of it moves with the breech, attached to the elevating structure, moving the “carousel” inside the other carousel, as seen in these 2 pictures, first facing forward, second slightly elevated, both from leftside of the gun.
(Note, these images are from the TM-9-1252 American document of the gun.)
War thunder does not model this properly (as far as i am aware, the LVKV 42 does not have a modified version of the LVAKAN M/48 autocannon. It’s difficult to see in war thunder due to the quality of the model, and due to the blur when you go close using Nvidia Ansel as i have done it, but the hole in the back of the breech where the Bofors cannon ejects the shells is simply cut off, replaced with a panel and some circle.
This is the hard part to see, but the “carousel” is modelled properly, however attached to the bottom of the cannon with no visible way of ejecting the shell.
As you can see in this illustration from TM-9-252, once again an American document on several bofors L/60 import variants, the rear cover has a hole to eject the shells.
Furthermore, in this part from a US navy training video i couldn’t find the name of, you can see the spent casing getting ejected out the back, using mechanics that wouldn’t allow a mechanism to eject it downward without changing the entire breech function.
Sources for the documents was Gene Slovers US Navy pages website (Gene Slover's Navy Pages Home)
All media but the training video (too large to upload) are available here:
lvkv 42 problem.zip (19.3 MB)