Like I said earlier, I have no doubt that the PTRD could disable a Tiger or Panther, and I'm sure that it did happen at least once. But I doubt very much that it was a common tactic to attempt to shoot at out periscopes or optics.
I disagree. Here's why, straight out of the PTRD manual
http://www.battlefield.ru/index.php?option=com_content&task=view&id=280&Itemid=123
PTRD manual said:
Vulnerable spots on tanks (armored vehicles)
The most vulnerable spots of tanks are: their flanks (fuel cells), drive sprocket, sights, vision devices, and rear hull (engine compartment); of armored vehicles - the engine, located in the forward portion of the vehicle.
When firing at the tank T-III aim as shown in figure 2.
Here's a couple of accounts on PTRDs being useful (someone asked for an account)
From
http://www.sudden-strike.ru/history/detail.php?ID=2754&print=Y
August 24 1942, Stalingrad (consider early or late war? Dunno tank type unfortunately)
Four tanks down by PTRD used by untrained soldier (radioman or political officer)
"here Yevtifeyev took aim, went
down cock. Shot occurred, but front tank did not stop. For
the second time took aim. Shot burst out, tank began to rattle,
smoke released, and then it stopped. - it lined... it lined... -
soldiers joyfully addressed... Still they gave two shots, and
two additional tanks lined. On the fifth shot the oversight
left. Did not fall Yevtifeyev. It hurried. By the
sixth cartridge Of evtifeyev nailed to the earth the fourth tank."
Tiger vulnerable
"During January 1943,
attempting to close the breach of Soviet troops at the Volkhov Front,
Germans threw in the battle the newest tanks T -.VI"Tigr". These
machines then there were the schitannye units. They underwent
troop tests, so that it would be possible to consider experience of
their operating and combat use in the construction of series machine.
And here with this "tiger" entered the single combat the
antitank riflemen of Volkhov Front. By well-aimed shots they
derived from the system all inspection systems of tank. Crew
stupefied by this ran, after throwing almost proper machine.
Without desiring to leave it in the hands of the Red Army,
Germans opened fire on their machine and undertook even several
attacks. But our repulsed tank and drove away to show it
specialists. After several months to the Kursk battle all
vulnerable places of "tigers" were known."
By the way, I can't find any post by a "wonderboy" supporting hitting the optics should blow up tanks.