The .40 Smith & Wesson cartridge was developed out of the FBI’s dalliance with 10mm ammo handguns and law enforcement agencies are still questioning the 10mm’s place in law enforcement.
Here is a brief history of the FBI’s relationship with 10mm ammo:
- A Miami shooter in April 1986 led to ammo and penetration tests for the FBI
- Due to incessant problems with the S&W Model 1076, the FBI’s relationship with the 10mm was short-lived.
- 10 mm ammo proved too expensive and difficult to shoot, which led to the development of the .40 Smith and Wesson cartridge.
Why Did The FBI Test The 10mm Handgun?
After an initial inquiry by the FBI to determine how their equipment and training performed. As a result of the investigation, one major flaw was uncovered: the ammunition’s performance. Before that time, penetration was not considered as important as expansion. However, it became evident that penetration was a major factor. The result was the three-day Wound Ballistic Workshop of 1987. The event consisted of ballistic experts, medical examiners, and top law officials. The workshop's findings were helped to outline criteria for ammunition selection, which favored penetration of 12 or more inches. As a result, the 9mm Winchester 147 grain hollowpoint was adopted by the bureau.Â

The 147 grain has gone through extensive military testing and has since been adopted by the FBI for all 9mm weapons. The 147 grain subsonic, however, replaced the load even though it performed excellently.
The FBI continued to do extensive testing on their load sizes and it soon became evident that the .40 caliber/10mm, which is the exact middle-ground between the .45 and the 9mm, was the ideal round. As a result of the testing, the FBI adopted the 10mm round, at about 950 fps.
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