What will break bullet proof glass?

Bullet-resistant glass is designed to withstand specific threats, but it is not indestructible. Repeated impacts from firearms in the same area will eventually weaken and break it. Higher-caliber ammunition or specialized armor-piercing rounds, exceeding the glass's specific rating, can also penetrate it. Extreme non-ballistic force, such as powerful explosives or heavy demolition tools, will also cause it to fail.