Somebody mentioned that a 50 cal will go right threw the engine block of the 190 with AP rounds, atleast if I understood it right.
That is SOO wrong, there are about no rounds wich would penetrate the whole engine and go threw it, AP or no AP. The armored glass in the 190 was made specificly to stop MG and heavy MG (50 cal) fire from fairly close range, it deflected the shots thanks to a good angle and it consisted of 50mm armored glass. It DID in many caes stop the 50 cal bullets, even at close ranges. the 190 A8/R8, sturmbock version of the 190 A8, had extra armor (not more glass though) and it was used to fly in behind the bombers, quite slow, line up behind them and not fire untill the leader gave the command. They flew in V formation and they usually opened up at about 100-200 meters. The armored glass stopped bullets from hitting the pilot, the extra armored plates in the wings protected the guns, the extra armor around teh engine and around the cockpit stopped bullets from there (of course engine was vulnerable anyway, it was just a ring around it).
The Sturmbock squads usually didnt loose any planes in these attacksm when they did, they usually didn't lose more then 1 or 2.
Remember, they did this in group of about 9 planes, and they attacked 100+ B17's whom most, not all, were shooting at them.