Another way possibly could be:

- if you use models, you can assign a skill to each type of object like my._typeID = 1 for wood textured objects, and my._typeID = 2 for metal textured objects. Then just use that information in the event - if(event_type == event_entity)&&(you._typeID == 1), remove the bullet, if you._typeID == 2) just bounce.
Its another idea