Wait,that circle thingy in the bottom of the shell exist after round being fired? I thought that's part of casing of a tank round?
One of the recap episodes in the main series, or some other supplementary material, says that (among other features) the tank shells have a microchip installed on them that is used to calculate the shell's velocity, trajectory, and angle of impact in order to determine the effect on an enemy tank. This and similar technology installed on the tanks themselves, plus the reduction of the shells' lethality and the modifications of the tanks' armor, basically turns tank combat into extreme laser tag.