There was a movie I watched that had a lot of people in a huge mansion/warehouse thing. The people were locked in and fought down till the last three for A lot of money. Once they got to the last 3 they each get a case and they all have a pistol in them on of the pistols isn't loaded.

The name of the movie is, House on Haunted Hill, make sure you get the original with Vincent Price, this movie is great