I have no clue how severe the effects with the MG/FF was on enemy planes in the Battle of Britain in reality, so I have no comparison for reality and modeled in-game.
I have to agree o nthe effects of the 20mm cannons in the Il-2 series. But I have no clue wehter that was close to reality or not as I stated above
.
The latest info on that was this website link posted here i nthe forums about the damage of WW2 rounds:
http://www.quarry.nildram.co.uk/WW2guneffect.htm