Is this for entry, or exit holes ?
Also, you'd need to decide where on the aircraft the holes are to be, and how they got there, from what angle, by which weapon(s) and, of course, which type of aircraft has been holed.
Sounds picky, but the angle, and calibre of the weapon, make a heck of a difference to the 'look' of both entry and exit holes, as does the range fired from, to some extent.
Entry holes, for example, are very often more of a 'slit', with the area around the 'hole', if on metal, normally being dented by the shock wave of the round. However, if the strike is 'square on', rare in air combat, then the hole could be neat and round, but probably still with 'dimpled' metal.
Whatever damage is required on a model invariably has to be done before construction, often working from both sides of the plastic, so some thought and planning is needed.