Very little damage will actually look like a bullet hole. Piglet's descriptions are apt in that the most you'll get is a sort of elongated oval. They will not be spread evenly either...both the target and the gun are moving very fast and at differing angles.
Exit wounds will normally appear larger than entry wounds, and will be affected by ricochet off internal surfaces as well as flattening out of the round. ALuminum surfaces will often extrude (even on entry strikes), and will appear as torn paper. The aluminum will bend before it tears, so there will be distortion in neighboring surfaces around the hole.
Fabric surfaces will rip away until they reach the next attachment point, where they may still rip, or partially rip.
Plexiglas will crack, at high altitudes may shatter completely
No airplane will be allowed to fly following any sort of battle damage until a thorough inspection is done and repairs made.
Some good battle damage photo's to go by....
View attachment 10880View attachment 10881View attachment 10882View attachment 10883
Note the wear along the wing on the 3rd photo....significant wear along the entire upper wing surface....interesting.....
Patches will be square riveted panels, usually off color from differing paints, levels of weather exposure, or simple lack of painting. Fabric will be painted (doped) but will be differing color as the paint wears quickly under UV. Plex will normally be completely replaced.