I drove a Sherman V today for some minutes on goodwood (something I usually never do, but a team mate was shot while repairing it and why let it going to waste). Anyway, a panzer IV is infront of me, I get one shot to the front, takes away about 80 percent of my health, I shoot too, get a hit indicator for the front and we both retreat behind something. I'd say it is definitely possible to harm a P4 from the front.
one shot to that panzer's cupola and he's so dead.
tips on busting tanks using 75mm
Stug : anywhere except front, don't waste reload time. Rather easy prey if they are too aggressive I'd say.
PzIVH : if you can't side-shot it(which is very rare), aim at the cupola. (that ugly thing on the turret), those are also easy to shot if you have some patience.
Marder : this one is made of paper, so fair match (!!!), these little stuffs, I have to add, is rather nasty because of their "narrowness"...
Panther : Frontal shots are not recommended at all, side shots and back shots don't really differ because you need 2 anyway. Since the panther would turn and kill you and you reload slower than that, unless you're camouflaged you need to MOVE.
Tiger : this one is tricky, but I'd only suggest you go shoot the side (wheels part), the back is almost as invulnerable to your rounds as the front. The turret
normally don't turn fast enough if you circle it close enough.
I found sweet spots on the pzIV and Panther's front but it's just too hard to hit them if they are 1+ grids away. And I never suggest anyone to go frontally against a tiger...