The 10mm was NOT developed specifically for the FBI. It was Norma's venture into creating a .40 pistol cartridge to be marketed generally. it shot flatter and carried more energy at longer range than the .45 and a tad more than the .38 WCF, which is what the .40 S&W almost matches. Sadly, since the '86 shoot FBI's firearms and cartridge choices are driven more by bureaucrats and some techs at the FTU ballistics test shop than by actual shooters or hunters. My agency fell in on the FBI's contract for the G19M and G2 147 gr load. Having shot animate objects with both our "old" 124 Hydra Shok and the Speer G2 the Federal bullet proved more destructive in my experience. The race to the 9mm was partially driven by some definite improvements in projectile construction but largely by agencies more interested in "diversifying" their organizations than training men and women to survive a fight. All the hooplah about this recoil thing in pistol cartridges has been used as an excuse to permit the hiring of people who are not suited by either character or temperament to do the job. Remember that all agencies have qualification scores that are set as a benchmark for job performance but "qualified" is in no way related in reality to "proficient". The modern FBI sadly has become a notorious box checking organization for too many things, from certifying agents regarding the Attorney General's investigative guidelines to marksmanship and gun handling. The 10mm as originally fielded by Norma and launched in the Bren Ten and Colt Delta Elite was a terrific cartridge that the FBI caused the neutering of and the invention of the .40 S&W or "attenuated 10" as the good Colonel called it. But all praise to Paul Liebenberg for designing the first .40 S&W for Smith, a task many said could not be done efficiently.