remember, there are things between you and the bullet, including glass, fuselage, etc.
I remember reading a story of one of the members of the Black Sheep squadron (may have been Pappy himself) that a Japanese 20mm round had gone into the cockpit but had lost enough kinetic energy (probably went through fuselage) but ricocheted off something inside the cockpit and landed in the shoe/boot of the pilot.
Basic moral of the story is, yes a direct hit from a high caliber round will kill, but only chance for direct hit is in an I-16. Also, .50's are not the only MG round in the game. 7.7mm and .303's are far smaller and have less stopping power on a human being (yes there is still stopping power, but just not as much)
I spent around 25 years around aircraft, both military and civilian. I wouldn't trust in the ability of
almost any aircraft to "slow down" a 50 cal BMG round. Adding to the carnage is the common use of
armor piercing incendiary ammunition which wouldn't even notice the aluminum fuselage.
It might hesitate at the cockpit armor, but at 200-400 yards, I wouldn't bet on it. I certainly
wouldn't consider glass an effective protection system as well. You tend to hear about the lucky
guys who survived close calls....the ones that didn't aren't quite so vocal. Getting hit by a high
velocity 30 caliber is not exactly minor either.
The ranges commonly used in AH are very close for the weapons used. Which means the velocity
and penetration would still be relatively high.