Meh, averages don't tell you too much, because while, say, 75% might get a hit percentage of 12%, say the other 25% fires of hundreds of thousands of rounds and never hits squat (HOs, spraying 1.5k, firing as they die, spiraling down, toolshed strafing), so I think that percentage is being dragged way down by the "low end".
In worse guns, with the 190E, I myself have gotten 3 b17 kills in 1 sortie (still had 21 rds of 20mm left) and 3 spitfire kills in 1 sortie (2x spit16 1x spit8) and had to rtb for lack of 20mm, and all the while my gunnery sucks. I take pot shots and bursts that don't land all the time. I screw myself over because of this but I'm a lucky SOB so I usually come out all right in the end (2:1 k/d this past tour).
So if I can get multiple 3-kill-sorties on a plane with 120 rounds of 20mm but worst ballistics, anybody in a much more manuverable plane with better guns can too.