I am retired from IATSE local 21 newark. worked 34 years. We used Real firearms on the shows that require firearms. Most were donated, Papermill theater before fire in 82 or so. Had colt pythons, 03a3s, some levers. Who knew who owned them. Used blanks, But REAL firearms. ATF only got involved with a license when there was explosives used. Pyros for concerts was NUTS!!!
Unless the manufacture “prop” guns with special chambers that can not fit a round with a bullet, I suspect they are capable of firing live rounds. But if its possible to have metal fragments lodged in the barrel, someone needs to design new prop firearms. Or do really complex CGI.