Dumb never dies, err, wait...
http://www.nbcnews.com/news/us-news/teen-youtuber-shoots-kills-boyfriend-video-stunt-n777851
She claims it was his idea and he talked her into it.
That's got to be a Darwin Award winner.
Clearly he hadn't heard of the concept of a "dry run"
Apparently they did several dry runs, according to the article. Apparently she had been practicing on various books and showed him one that the bullet didn't penetrate.
The "trick" seems like it would work, in practice. However, so many things can wrong... You could two books with identical page counts and one would block the bullet and the other wouldn't, depending on the thickness, type, humidity and age of the paper and the thickness and material of the hardcover itself!
That's not even counting the ammunition! Depending on the age, storage humidity, brand and several other factors the speed of the fired bullet can vary several hundred FPS.
There's also a matter of if she used JHP or FMJ rounds both times. A book might easily stop a hollow point, because it mushrooms and fragments on impact, dissipating much of the energy; whereas a FMJ, especially a .50 caliber(!), would punch right through a book like it was cheese cloth.
If a professional were to perform a stunt like this, they would load their own ammunition (or have it loaded), using only a tiny amount of powder (to limit the bullet's energy), use frangible ammunition and wear Kevlar (or replace the back panel of the book with Kevlar).
The fact she couldn't foresee how something would go wrong is mind boggling to me.
A god damned Desert Eagle. Seriously.