Steps on how to make glass breakable instead of bullets going through?

This guide explains every step that's necessary to set up glass collisions properly:

Guide

Glass Collisions

This guide summarizes the most important points to set up glass collisions correctly.

I have merged your new thread into your existing one, as it's the same issue.

If all properties are set up properly as explained in the guide, there are likely issues with the mesh or the collision mesh itself. It could have improper positioning (for example caused by shifted axes, both for the objects themselves or parent nodes), or the collision mesh itself could be faulty in some way. To test if that's the case, I'd recommend importing the collision from one of the default cars from the game to replace your collision.

Not the full glass, only the collision, which is named glass_something [COL]. It's easier if you use a similar car, but you'll have to reposition it either way. You'd either import the whole car and take the parts you need, or export only the glass with its collisions and import that.

It's unlikely that the mesh is the reason after you've imported one from a default car and made sure that the crash property and IDs are set.

Based on my experience, the easiest step from the guide to miss is the crash property for all the window materials. Windows have multiple materials, typically at least an inner and an outer glass, and possibly depending on the importing process with the hi and standard yfts 2 of each.

Make sure you are changing the ID state in external, so step by stepthe way I do it is, hide all - find and show window cols - remove any crash in user define and the used glass material(If you do not want bullet impact animation) - highlight all window cols - polygon mode - highlight all polygons - properties - external state - ID change to 123 - Apply