Barney has a tendency to shoot his gun, so Andy makes him keep his bullet in his shirt pocket. Sometimes, however, the bullet gets into the gun and Barney shoots it. Andy then holds out his hand, and Barney reluctantly gives the gun up for a while. He sometimes uses the excuse that it was getting green in his pocket, or he lost it in the laundry.
In Andy and the Gentleman Crook, Andy fires the gun by accident.