I was in the play "Oklahoma" when I was in high school. We used my shotgun in the play and to ensure that nothing could happen I made 2 wooden plugs to fit the chambers. I used wood dowel rod and made them so I could beat them in with a hammer. The plugs were made so that they would squeeze down in the forcing cone and were about 1/2" below the rim cuts. They were tightly in place and after it's prop duty was finished, I knocked them out with a cleaning rod. It was a different time!