The FBI's short history with the 10mm was accomplished with S&W's large framed Model 1076 pistol - the Glock 10mm had yet to be developed.
The 10mm was downloaded for two reasons: The control factor and the fact that the full-power loads over expanded and didn't penetrate like they wanted. They backed off the velocity about 200 fps - expansion decreased - and the desirable amount of penetration was achieved.
It was only then that someone had the bright idea that there might be a market for a .40 caliber cartridge in a 9mm sized pistol. After all, if you're going to limit yourself to a 180 gr bullet @ 1000 fps, that can be accomplished with a smaller pistol that holds more rounds.
