The Waco Tribune-Herald newspaper reported on Friday that Sgt. Heath Vanek would miss at least two months of work because of the injury.
Vanek reportedly hurt himself on July 15 on his family's property as he was teaching family members how to clear the chamber of a semi-automatic pistol if it jams.
Hewitt Police Chief Jim Devlin told the newspaper he spoke briefly with the 11-year veteran after the accident.
"He said, 'I made a classic mistake,'" the chief told the paper. "We are human, too. We are not infallible. We make mistakes, and when we mess up, we mess up and do our best to correct it and get back to giving the public the best service we can."