jbroey, have you even fired a real gun in your life Even then have you ever fired a gun at something other than paper targets?
Because while I notice that your trying to sound like you know alot about ballistics and weaponry, but your just showing your ignorance.
Take your average .22 caliber rifle out to a field somewhere and shoot at a coffee can with it. Fire a couple hundred rounds at one hundred yards and tell me how many bounce off. And then realize that a heavy machine gun round or a 20mm cannon round literally has thousands of times the force.
Even rifle caliber rounds such as the 7.62 NATO (effectively the same as the .30 caliber machine gun round) will punch thru an engine block of most cars. How do I know? I've done it. A .50 caliber round will go thru both sides of armored cars. And I won't even get into 20mm AP rounds. And FYI, even that very small .22 caliber round is lethal up to several miles.
Now go study what an airplane is made of, yup thats right, Aluminum. Very thin aluminum. In fact you can punch thru the skin of most aircraft with a screw driver or knife easier than you can that coffee can. Even the frames of aircraft were stressed steel tubing, which wouldn't deflect rounds except in very extreme cases and would still heavily damage the structure.
Aircraft are very delicate machines.
Armor you say? Go check a diagram on aircraft armor and you will see that very little area on an aircraft is armored. I can provide several if you don't have any handy. Usually just the pilots seatback, the forward viewscreen, portions of the firewall, and maybe small especially vulnerable area's such as the oil cooler and the 30mm ammo bin. Not much at all, and usually its not thick enough to stop HMG rounds and higher (.50's and up).
Show me guncamera footage of rounds bouncing off (and if you think you find some, watch closer, because most likely its chunks of plane coming off).
Just because IL2 does it, doesn't mean its real.
I've tried to keep this discussion simple, but if you'd rather we can pull out ballistic coefficents and other physical characteristics, force equations, and Finite Element Analysis simulations.
You see.... Aircraft guns, ballistics, and lethality are a hobby of mine. I'm no expert like Tony Williams who posts here regularly (author of the book "Rapid Fire"), but I do know enough to call roadkill when I see it.