Also do not forget if you wanted real ammo loads, T-72 would get 30 rounds for the 12,7mm MG or so...
This is worthy of another idea though - the .50 weapons usually have pretty low practical RoF and ammo supply, either mobile or mounted, OTOH according to some British study the suppression effect of .50 is HUGE compared to 5.56 and 7.62 (which are not that far away)... Thought of trying to give .50s a WH size of 2 so that they have a different graphic (AC) and bigger suppression (and HE penetration) compared to rifle caliber weapons.
BTW also tried a similar approach with snipers, giving the sniper rifle a class of 2 (so that you can do say a sniper team without everyone in the team firing the sniper rifle) and WH 4 (to create a beaten zone) with HE kill of 1... My reasoning was that snipers were also pretty suppressive weapons and that their suppressive effect was often far bigger than factual.