Bobblehead - Big Guns

 is one of a total of twenty Vault Boy Bobbleheads found throughout Fallout 3. It permanently improves your character's Big Guns skill by 10, to a maximum of 100. The inscription on its base reads "The best way to win an argument is to be the loudest".

Location
In the basement of Fort Constantine's CO Quarters. To reach it kill the protectron which is usually found there and the procede down into the basement. As you go down you will see a open safe on your left (literally open, not just one which has been unlocked). The bobblehead is in the safe along with some caps.
 * http://www.youtube.com/watch?v=1IcgHfX2Wlo