Actually, cupola-mounted MGs would be more than accurate, since most German tanks had a mount for one. Its main purpose was anti-aircraft.
But, that's the problem of implementing them - to be perfectly accurate, only German tanks would have them until the advent of the IS-2, which got a big honkin- 12.7 mm Dushka. Now I know that there are a lot of Panzer commanders out there who would love that MG34 or MG42 just sitting up there ready to waste clown cars, but I don't remember seeing any T34 with one (some BT-7s had them, but only early ones).
And PLEASE, stop thinking that anyone is going to shoot through an armored vision block. If anyone missed it, the proper name for "those little slits that you see through" is armored vision block. There are rare instances of direct strikes with PTRD rounds that would penetrate enough to send shards into the faces of gunners or commanders, but a PTRD is an anti-tank weapon - not just a rifle.
And for the record, it didn't work for Tom Hanks either. His was futile last shots were coincident to that P-51 actually blowing the tank up. So there.