This cant be realistic - 500+ hits, plane still flying??

[Avimimus]

The sim also models bullet speeds - they quickly drop into the subsonic range and then gradually slow from there. This means that close range shots have supersonic bullets with a lot more KE than medium range shots. In Il-2 this amounted to about three times the effectiveness. Ideally you want to be within 30 metres of your target before you start firing (unless it is a head on attack!)

This isn't really an issue with cannons - since the rounds detonate on impact (creating supersonic shrapnel).