Just for the sake of this thread 
http://bbs.hitechcreations.com/smf/index.php/topic,256729.msg3178668/topicseen.html#msg3178668
Film:
http://www.mediafire.com/?tjzmzh3tzg5
30mm hits all over and it just flies away.
(Image removed from quote.)
(Image removed from quote.)
Buffs are another story entirely
Lotta evidence of them taking massive damage only to be able to RTB.
(I wish the damage to the buffs in game was visually better addressed.)
These planes made it home
20 mil damage
Enemy 20mm cannon hits ignited electrical equipment in the nose of "Belle of Maryland", including the pilot's instrument panel. Numerous fire extinguishers barely kept the fire under control until landing (with a burning engine as well). As soon as the B-17 came to a stop the nose erupted in flames, and while the crew escaped safely, the bomber was ruined beyond repair.
Source: Mighty Eighth War Diary by Roger A. Freeman

Tinkertoy, 'jinx ship' of the 381st BG, after the October 8, 1943 mission to Bremen, Germany. Men point to holes made by 20mm cannon shells which decapitated the pilot.
SOURCE: The Mighty Eighth by Roger A. Freeman

A German 20mm shell peeled the metal covering off this bomber like skin off an onion. Note the small caliber bullet holes in the fuselage star.
SOURCE: Target: Germany by Life Magazine

This ball turret shows the effect of a 20mm shell which exploded against the faceplate. The gunner was wounded, but survived the jarring blast.
Text and photo source: Air Classics magazine, July 1972

According to a visitor (Patrick), this is a B17G (build by Lockeed Vega in California) 42-39988 QJ-A from the 96th BG, called "The Iron Ass", flown by 1st Lt Paul Herring. She was damaged by FW190 during a mission to Brunswick on the 21st February 1944. The crew member near the hole is Charles (Chuck) Haywood, the tail gunner of this plane. He was shot down four days later, flying with another crew. The Herring crew was shot down eight days later, flying B17F 42-30412 QJ-B "Mischief Maker"; they were on their 15th mission.


What happened here? Duel For the Sky (by Herbert Molloy Mason, Jr.) states that an Me-262's heavy cannon tore open the side of this Fortress, but according to the Mighty Eighth War Diary (by Roger A. Freeman) the B-17 was hit by an 88mm shell , blasting a special radio operator and the ball turret gunner in his turret out of the aircraft.

This is just stuff from fighter damage.
More damage of planes that RTB from larger caliber stuff (88's) here
http://www.daveswarbirds.com/b-17/contents.htm