There are five chambers.

After the shooting the chambers were emptied and the unused shells returned to the box.

Here is the box." This time Britz offered Collins a small pasteboard box, but Collins shrank from it as if afraid it might explode in his hand.
"You will observe," Britz went on, "that there are forty-nine cartridges left in the box.

One is missing--the one that was exploded.

Now Collins"-- the detective's jaw snapped viciously--"you've decided to remain silent! Well, I've shown you some mute witnesses whose testimony will be understood perfectly by a jury." All the blood had drained from Collins's face.