The gun case is a storage container found in Fallout 3, and Fallout: New Vegas.
A gun case is one of the many item storage units in the game. It is not as common as the usual locker variants, but isn't rare. As the name implies, it usually has guns in it, and like most containers the items found within can vary between different games. They are labeled as gun cases and they look like the normal footlocker, or the larger counterpart that stands upright, much like a locker.