Nice pictures of battle damage. I guess the bigger holes do indeed come from the projectiles striking at an angle as Sutts says.
You can see that they are not so round but elliptical in shape, indicative of a line of travel more or less parallel to the fuselage at the time of impact which results in "dragging" more of the fuselage skin along with the bullet as it penetrates.
Perfectly round holes on the other hand would be due to impact at a near 90 degree angle to the fuselage.
Finally, their appearance could also be slightly affected by the camera's viewpoint/orientation in relation to them when taking the picture.
Always nice to go on a collective hunt for the small details