The FBI is Going 9mm: Here Comes the Science | The Loadout Room This information was published by Loose Rounds on September 21, 2014. After the Miami Shootout in 1986, the FBI invented modern ammunition testing and led the law-enforcement movement to .40 caliber. The FBI is very conservative, and has one of the best ballistics labs in the world. With the amazing 21st-century advances in ammunition technology, many people have advocated a move back to 9mm. Recently, the FBI announced they were buying a new gun in 9mm. When the FBI makes a move like that, they have thought it through very thoroughly.