Well that would be 10-25 hits out of a burst of 480 bullets. Not really a lot...
I wouldn't expect wings coming off and the such.
( From:
http://www.quarry.nildram.co.uk/WW2guneffect.htm "
estimates for an average pilot's hit rate varying between two and five percent").
With only 10-20% of incendiaries causing fires don't expect too many fires either.
From reading about Hartmann, Knoke and Sakro it seems they shot well inside 200 yards, in real life.
As said I fly the Hayabusa in IL-2, attacks are never from dead 6 however - IL-2 rear gunners would kill you with the blink of an eye if you do that - and it's two 0.303 are effective if used properly - meaning to hit in the first place and from close distance in one particular area, with an angle.
I remember that even back then people where complaining about 0.303 not being effective enough.
I tried once the 8 gun hurricane against He 111 and Ju 88, what an awesome firepower that thing had compared to my little Hayabusa and no trouble in shooting down German twin engines.
Maybe we are expecting to many big bang explosions, wings coming off, fires all over the place.
Now how is it in CoD, if you shoot at 100m or less, not from dead 6, difficult to shoot down planes?
If I watch vids like this it seems 0.303 is effective: