It was actually created in response to the FBI’s desire to
have a more effective round for semi-auto guns. In April of 1986, agents with
the FBI found themselves being pinned down by automatic rifle fire by two bank
robbers in Miami. Though the agents outnumbered the robbers, their inability to
counter the firing rate proved to be fatal for two agents. Not to mention that
the robbers were both hit multiple times, yet still had the ability to shoot
their own weapons.
In response to this, the FBI commissioned S&W to develop
a round that could surpass the effectiveness of their .38 special, which was
their standard carry weapon. The FBI wanted their new round to have increased
stopping power but still have low recoil for more accurate consistent firing. The
first round created was the 10mm, but it had more recoil and required a bigger
gun than the FBI want. The two companies, after several rounds of testing,
created the .40 caliber intended to be used by Law Enforcement agencies, though
many, today, are moving to the 9mm.