OK, let's start with the demise of the P91. Actually, the P91 was good pistol, just a victim of timing. The development of the the P93 and P94 (both 9mm and .40 S&W) was just getting underway about the time the P91 was released. The P93 and P94 were originally intended to replace the P89 and P91. The .40 cal at that time was the poorest selling of the 'P' series calibers, accounting for only a small percentage of the overall sales. The lion's share went to the 9mm, followed by the .45 ACP. It was determined that with the introduction of the P94 (.40 cal), the P91 would no longer be a viable product financially. The sales of the P89 remained high even after the introduction of the P93 and P94 so it was retained. Without the P91, the public's only choice if they wanted a Ruger .40 was the P94. There was never anything wrong with the P91, it was just a victim of the redesign to the P93, P94 configuration.
As for the development of the .40 S&W, this information came to me through a friend in the ammunition industry.
When the FBI determined the 10mm was too much gun for the average agent to handle, they requested a reduced load, something hotter than a 9mm and about equivalent to the .45 in power. But they wanted to retain the higher capacity that the smaller diameter cartridge would allow with a double column magazine. I don't know who their ammunition supplier was, but in conjunction with S&W they decided that with the reduced load, they no longer needed the long case of the 10mm and could make a .40 cal cartridge with the same OAL as the 9mm and put it on the 9mm platform. However, they wanted to retain the heavier bullet weights. Thus came the truncated cone bullet shape for two reasons. One, the cartridge was quite similar to the 9mm and to make it easier to differentiate between the two cartridges, they didn't want a round nose bullet as with 9mm ball ammo. Also, to keep the heavy bullet weight and yet have sufficient case volume they couldn't have a round nose, it would make the cartridge too long.
The only problem was that the truncated cone shape was difficult to feed. The firearm manufacturers did various things like deepen feed ramps, thus reducing case head support, or making their chambers oversize allowing for excessive case expansion to get their guns to feed. After a short time on the market they started receiving many complaints about case head separation. Many loading manuals added a note to their .40 cal data cautioning the loader to contact the firearm manufacturer to ask if the case head was fully supported. To obtain the required performance, the cases were being pushed to the limit. Then when sombody tried to reload it back to factory specs, they blew case heads. The ammo manufacturers immediately jumped on the issue and redesigned their .40 cal cases. They are all on their 2nd generation cases with a few on their 3rd generation case. Ever wonder why you don't see a +P loading for the .40 like you do for the 9mm or .45? That's why. The normal load is as hot as they can go and retain case integrety. Very few manufacturers operate their ammo at SAAMI spec. They tend to keep the loadings fairly light. Exceptions being the +P, +P+ and military loads.
The bottom line is that the .40 cal was rushed into existance without sufficient development time. The SAAMI spec for the .40 is 35,000 psi as is the 9mm, but with the larger dia cross section and heavier bullets, the impulse was significantly higher as they had to operate at SAAMI spec to get the required performance. The .40 is harder on a gun than the .45 due to its heavy bullets and high operating pressure. The impulse isn't really all that high, but if you break it down mathematically into its force and time factors, the energy is dissipated over a considerably shorter time than the 9mm or .45 thus transferring more of it to the gun. A .45 platform would be more appropriate for the .40 than the 9mm, that is of course, unless the 9mm was beefed up to handle the additional stresses incurred. I'm sure those of you that shoot both the .40 and .45 have noticed that the perceived recoil of the .40 is much snappier than the .45. That is the result of the rapid transfer of impulse energy to the gun.
That's pretty much the story of the .40 S&W as was told to me and also what I've seen during the development of .40 cal pistols. Some of you may have more info or some questions. Please feel free to add your 2 cents worth.
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