In the aftermath of the 1986 FBI Miami shootout , in which two FBI special agents were killed and five wounded , the FBI started the process of testing 9 × 19 mm Parabellum and .45 ACP ammunition in preparation to replace its standard-issue revolver with a semi-automatic pistol . The semi-automatic pistol offered two advantages over the revolver : increased ammunition capacity and increased ease of reloading during a gunfight . The FBI was satisfied with the performance of its .38 Special P lead semi-wadcutter hollowpoint ( LSWCHP ) cartridge ( " FBI load " ) based on decades of dependable performance . Ammunition for the new semi-automatic pistol had to deliver terminal performance equal or superior to the .38 Special FBI load . The FBI developed a series of practically oriented tests involving eight test events that they believed reasonably represented the kinds of situations that FBI agents commonly encountered in shooting incidents
1986 FBI Miami shootout
1986 FBI Miami shootout
.40 S&W