Happened to came across this thread, would like to share my unusual battle damage piece.
This is a piece from a downed Japanese Mitsubishi Zero Type 22 on one of the islands of the pacific. Not sure the exact part, but it's on the starboard of the cockpit.
It has a believe to be a 12.7mm (.05 cal) machine gun or a 20 mm cannon bullet penetrated damage. A very dramatic aircraft related artifact.