This thread is meant for bug reporting of Bf 110C series bugs for the developers.
I couldn't test them yet, but it appers that both C-4 and C-7 have the old MG FF 20mm cannons instead of the MG FF/M they had historically (C-2 had the MG FF). The FF/M could fire the special, high capacity Minengeschoss HE shells with thin shell walls, which carried considerably greater amount of explosive fillers than normal HE rounds (about 3 times the amount).
I did not have any time for performance testing, but if somebody is inclined to do so, here are the original Bf 110C-2 datasheet from April 1940, a courtresy of G.G. Hopp. Performance of C-2 should be identical to C-4 (only difference being the newer model of the same gun, which weighted the same).