Difficult to estimate its size but looks like a bullet hole to me, definitely bigger than 9 mm.Posted by SilentFeathers (here)
Many of these holes I've seen in the several photos posted in this thread almost look to me as if they are "bullet holes", such as 30 or 50 cal., but I am no expert.
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It looks like it came from a anti-clockwise rifled barrel.
This part must have been inside the plane ... if it was shot from outside then this is the
2nd or 3rd penetration.