Developed by Smith & Wesson and Winchester Ammunition and standardized in 1990, the 40 S&W is a fascinating case for several reasons. Developed to offer law enforcement more fight-stopping capability, when compared to the 9mm Luger, in a smaller package, when compared to the 45 ACP, it took only 60 days from a request by the FBI until the first prototype pistols and ammunition were tested! In the world of commercial cartridge and gun development that represents unheard of speed, positively tornadic! While the 40 S&W has gained widespread acceptance and it certainly is an effective fight stopper most folks can learn to handle; after all, ballistically, it entirely duplicated the revolver round Elmer Keith (of 44 Magnum fame) and others had petitioned for a generation earlier, it came about because of a tragedy. In the 1980s, the FBI was looking to standardize a sidearm for its agents with a pistol that was smaller, handier, and easier for most to gain proficiency with, compared to the 45 Automatic in the 1911 Colt and more modern than the passé 357 Magnum revolver. Word came down from on high that the FBI wanted to standardize issue guns so all agents would carry a pistol of the same chambering. It had determined that, with modern ammunition using efficient expanding bullets, the 9mm Luger was entirely and totally adequate. So, junior FBI agents were issued new guns to use on duty. Almost instantly thereafter, a now infamous gunfight occurred outside Miami, Florida. The first shot fired by an FBI agent was perfectly placed, it hit the bad guy in the sternum and should have instantly taken him out of the fight. Had that been a bullet from a 45 Automatic or a 357 Magnum, it would have. But, that light bullet over-expanded and stopped on the surface of his heart. The bad guy then proceeded to kill several good guys and was the last man standing when that fight-for-life ended. The FBI had a problem. It could hardy recommend its agents switch back to their 357 revolvers or use a 45 Automatic pistol and thereby at least tacitly admit it had been wrong to recommend and issue 9mm pistols, a decision that had resulted in the death of several law-enforcement agents; but, it was obvious a firestorm was about to ensue as word got out and other agents realized their lives were in danger because of the obviously, demonstrated to be, inadequate guns and ammunition they were saddled with. The solution was to invent something that would do what the 45 ACP would do in a smaller package and issue that to replace the 9mm pistols — hence, the 40 S&W. As with any pistol round headspacing on the case mouth, best practice is to apply a taper-crimp after seating the bullet. This helps to lock the bullet in place against chambering forces that might otherwise drive it into the case. I cannot too-strongly recommend getting a second seating-and-crimping die so you can have one adjusted to only seat the bullet and the second adjusted to only taper-crimp the case mouth. Generally, attempting to do both operations in one step is a recipe for damaged and destroyed cases.