Here is a wonderful animation of a Beretta 92FS. I have spent much time studying to fully understand the mechanics of its workings.
http://www.genitron.com/Basics...ctive-Beretta-Pistol

Here is another which shows a Glock and the tilting barrel system as used in the Sig.
http://www.genitron.com/Basics...ractive-Glock-Pistol