Turns out the problem really is RNG

golruul, on Jul 10 2019 - 23:14, said:   Flarvin explained it, but I'll give another example.  Average (stated) damage is 490 for that gun.  However, let's say you only shoot at tanks that have 489 hp or less.  If you always do this, you will never get an average damage or higher shot (because enemies only have 489 hp max).  If you then make a note of all hits and calculate your average damage per penetrating hit, it will be way lower than 490.   Basically you need to ensure each one of your shots has the opportunity to be able to do the full spread of damage each hit.  If you don't, your averages will be messed up.