Fun thing to keep in mind about vehicle crits in the new patch:
Because Relic screwed up the crit tables, vehicles are GUARANTEED to receive main gun destroyed from any small arms or flame damage that penetrates below 25% health. Even an IS2's gun isn't safe from the massive destructive power of MG42 incendiary rounds from the rear.
Ballistic and explosive damage correctly applies the main gun crit only 10% of the time.
I assume this includes PTRS as well? Gotta keep that Guards meta going strong!