There isn't (unless I've somehow missed it, multiple times now) any sort of rule for composite armor on vehicles, correct? Most HEAT rounds have fairly equivalent stats to APFS versions, with the addition of an explosive blast characteristic, making them fundamentally as good or better in all situations against enemy armor.
Realistically, this is of course not the case, and HEAT rounds have been obsolete versus most modern tanks for some time (since the 1970s, really). Against their front armor especially, APFSDS rounds are the only viable option in most cases. And many older or light ATGWs and shoulder-fired rockets are totally ineffective against much of the front armor. Doesn't bother me too much, as this isn't a tank sim and I don't foresee my players driving a tank around shooting at other tanks very much... but it is "wrong" or at least a kind of important missed consideration, as well as one that emphasizes the significant qualitative differences between generations of tanks. Of course the portable AT weapon aspect gives dismounted PCs more of a fighting chance against a T-80, so maybe this is a balance concern? (But really the answer is "hide or run away!")
Another related thing: on all of the Soviet guns the HE rounds seem to have longer range than the others? Again, APFS rounds should have significantly higher velocity (and therefore range) in almost every case. This seems like a mistake to me, but maybe there's some logic to why that I just haven't thought of?