.40 S&W was made after a requirement for the FBI was posted due to the Platt and Matix case back in 86. One of the two was shot through the heart in the opening seconds of the gun battle, yet he went on to kill some 5 agents before finally bleeding out. The FBI was adamant it was the small caliber of their 38 Special revolvers that was the issue, not a lack of training. S&W received the contract to create a new bullet and gun that could use it. (This is where my information starts to get a bit hazy - been a few years since I heard the "behind the scenes" story. Ill update this should I find my info is slightly wrong. The premise still stands) This lead to the creation of the .40S&W. The FBI, however, wanted to use a round that was near-identical to the .40 - the 10mm. The 10mm and .40S&W work in the same guns, are the same sized bullet, similar enough casings, etc - similar to how .357 Magnum and 38 Special can be interchanged as long as your gun is rated to the higher pressures of the .357. However, the 10mm was such a "hot" round (industry term - meaning fast, powerful, lots of kick, etc) that many agents couldn't handle it. It also had issues in the upsized S&W 9mm guns S&W made for it. The FBI was unhappy and got into a massive legal battle with S&W over it. Long story short S&W won the case as the guns were built to the FBI's original specifications, and not the specifications of the 10mm. This lead to both calibers being available. In the end a .40S&W has very similar ballistic properties to a 9mm, but it kicks harder and puts far more stress on a gun than a 9mm. A "Race" style pistol like that would have issues with a .40S&W. A 10mm would be even worse. I know all this as my grandfather was actually a key witness for the case. He was with the FBI but left a bit before on an indefinite leave of absence to pursue his holster making business idea (what eventually became Rogers Holster Company, then HolsterOps and then a major part of Safariland). He also had his range and training that was being utilized by the US Gov for military training. As a part of the trial the judge ordered both groups to agree on an independent contractor to test the guns and ammo, and both parties were happy to use Rogers. It was something crazy that he and his team had to do - something like take 200 guns and test 500 rounds through each gun. He said they ended up wearing welding gloves and taping their wrists up with duct tape to get through it all. His findings were in line with S&W's argument, so the FBI actually lost that trial. The interesting thing about it all was - it wasnt the bullet that was the issue. Matix was a dead man regardless - no surgeon in the world could save him. But the shot could have been fired by any handgun up to and including a .44 Magnum or .50 AE, and the result would have been similar. The FBI training at the time was to fire a single shot into the torso within 1.5 seconds. If the officer had put all 5 rounds from his revolver into the chest, or even better tried for a headshot (the two were less than two feet apart. It would not have been a difficult shot...) things might have turned out different. There were a lot of other issues in that case that changed Bereau policies, but Im not going to get into them all here.