[potta_coffee]

I don't have a link, but I read a long article about the development process for the 10mm. Apparently, penetration was the reason they switched to 10 (and later 40). They were having difficulties with 9mm not penetrating windshields and other barriers.

[MrMember]

Yes, in the late 80s/early 90s 10mm was chosen by the FBI because 9mm ammo at the time had a tendency to under-penetrate (not an issue in the present day, 9mm today performs significantly better than 9mm 25 years ago).

The story of the FBI's switch from revolvers to semi autos is pretty interesting. They decided on 10mm but some agents found it to be too "hot" and had trouble controlling it. So they put out a request for a modified 10mm round and Smith and Wesson came up with the .40S&W. They developed the round before they had a production gun to shoot it, though. Glock had "acquired" some of S&W's new ammunition at a trade show to study it and found that by making minor modifications to their existing Glock 17 they could fire S&W's new ammo. They submitted the new gun to the FBI who chose it as the standard issue firearm for all of their agents.

[masonic]

  minor modifications to their existing Glock 17

I'm guessing you meant the Glock 20.

[MrMember]

The release of the Glock 22 predates the release of the Glock 20, but going by their naming convention the Glock 20 was patented first. It's possible they modified the 20 but I believe it was the 17, I would have to check the book where I read it (Glock: The Rise of America's Gun).