Isn't bullet proof 'glass' a bunch of thin laminated sheets? It seems like I read a long time ago that that was way stronger than 1 solid thick piece of glass or acrylic when it comes to stopping bullets, but way worse for fish tanks.
The above is from way back in the recesses of my already overcrowded and under-exercised brain, so it may be a figment of my imagination. Just be sure its a solid sheet before buying for aquarium use.