In fear of adding to the confusion - it is also possible to take damage from your OWN cannon at very close ranges. I caught this on film a while back. I was shooting at a plane that broke back into me as I fired. I kept the button down and he exploded a millisecond before we should have collided (on my end). On his end, we did collide, and I received a message saying so. My damage was - can you guess??
A pilot wound! I was originally quite confused. How could a pilot wound be caused by a collision (and the message said he collided with me). Slowing down the film showed cannon shells exploding on his fuselage just before I flew through his ashes and smoke. The film also showed the pilot wound occurred fractionally before the "merge".
It may well be that if you are firing cannon into the face of a C47 at zero range then you are shooting yourself down. A rare one for the purists anyway.
rgds