In the post An idiot and his gun, the author Sheldon was in more danger than he thought.
There's a new bullet proof glass that you can shoot through. It's been in use for a couple of years now.
It stops anything that inpacts it from one side and allows the person on the other side to shoot through it.
When the person on the inside shoots through it, the glass stays intact and leaves only a hole the size of the bullet. The rest of it stays intact. Even with multiple shots fired through it from the defenders side, it still retains it's physical properties and protects the shooter.