Gents,
It looks like everybody in this thread (and several previous ones on the same subject) agrees that the StuGs with 80mm front should be vulnerable to the Soviet 76.2mm up to 500m and is too strong as currently modeled in the game.
However, there is at least some information/opinions floating around which support the calculations of the good folks at Battlefront.
For example Thomas Jentz, who is by all accounts a very solid researcher, has repeatedly claimed that 80mm front Stugs and PzIVs were invulnerable to Soviet 76mm at normal combat ranges (reference - Osprey books "Sturmgeschuetz III and IV 1942 -45" and "Panzerkampfwagen IV Ausf. G, H and J 1942-45", pp. 21 and 20, respectively; when talking about Sherman's 75mm by invulnerability at normal combat ranges Jentz meant no penetration after 100mm; I assume that with regard to the 76.2 he probably meant a similar performance).
Another example: Niklas Zetterling, "Kursk 1943. A statistical analysis".While not a tank data book per se, it is a very well researched piece. Penetration tables at p. 213 show a weak penetration chance by 76.2 against PzIV front at around 250 m. Penetration estimates at p.213 credit the 76.2 mm. with 61mm.penetration only.
And if you look for sources giving penetration estimates rather than direct comparisons vs. PzIV armour, there is even more data suggesting that 76mm could punch through 80mm only at a much closer distance than 500m. If you look at the best sources available on the Internet,www.battlefield.ru and Guns vs Ammo they both show that 80mm penetration is reached at around 100m mark, not further. This is confirmed by the Russian's own estimates I have seen outside the Internet (my source here is "Entsyklopedia Otechestvoii Artillerii").
Exception to that is the APCR (BR 354P) which should indeed penetrate out to 500 m. But they seem to be capable of doing so in the game, the problem seems more like their availability.
So, summing up this rather long rant, I think there is a substantial amount of evidence (or at least some evidence) supporting the thesis that German 80mm fronts were proof against 76.2 Soviet guns beyond a very short range (Tungsten excepted). I am actually a little surprised that everyone here agrees otherwise. Having 80 mm Stugs and PzIV invulnerable to T-34s frontally is an attractive hypotesis in one aspect, namely it can explain some of the Germans' more lopsided exchange ratios vs the Soviets (ref. Prokhorovka - over 6:1 in tank losses!)and generally very good performance of the Stugs. It is difficult to explain otherwise, unless you subscribe to the theory that (1) all Germs were uebermenschen or (2) all Sovs were complete oafs - neither of which I believe. Replicating LSSAH's performance at Prokhorovka is difficult enough in CMBB. I don't see how you could do it without significant edge in equipment.
Cheers,
Zwolo