Ventilated holster...

[PRD1]

Originally Posted by Ron Wood

From your photos, if "a bullet passed through them", it must have been from a bb gun.
Ron

The appearance of the holes fits very well with the action of a bullet passing through a tough but resilient material: the central perforation reflects that portion of the material which is disintegrated/punched-out by the projectile, while the full diameter of the projectile is fairly closely approximated by the outside diameter of the area affected by its passage. The material closes somewhat after perforation, giving the appearance seen in the photos. The outside diameter of the affected areas in this case measures between .310" and .320", which agrees quite well with the common rifle calibers of the era.
Next time I get to the range, I think I will take an old holster or two and shoot it/them and see what the result is.

PRD1 - mhb - MIke