Whenever a bullet travels through a solid object, its velocity is changed. Glass is one example of this.
However, in ARMA 3, bullets travel through windows, completely unaffected.
See the following links for more details.
http://www.saf.org/LawReviews/Harper1.html
http://www.nrablog.com/post/2012/03/22/When-you-shoot-through-glass-this-can-happen-.aspx