Wiley Clapp tells us some about the .356 TSW. It was developed for competition by S&W. The TSW meant Team Smith & Wesson. It was a proprietary cartridge chambered in guns made by S&W.
The idea was a common one at the time and went to an issue, or aimed at resolving an issue, in both IPSC and USPSA. That issue related to power factors and the difference between major and minor categories in competitive shooting.
Up until 1996 or so to make Major you had to have a power Factor of 175. PF was set by taking the bullet weight times the velocity and dividing that by 1,000. A PF of 175 or above was major and below that was minor. This favored heavier bullets.
Now there were other things going on the competitive shooting at the time that developed into issues and that shooters have tried to resolve but I can't get into that in a post. So...
Folks figured out that if you took the 38 Super cartridge and loaded it up you could make major. This was true especially in guns with compensators. You could do this with a heavier or lighter bullet, either way. As 38 Super is essentially a 9mm cartridge you had increased mag capacity over the 45 acp and less recoil with a lighter bullet especially with a compensator. So 38 Super came to dominate competitive run and gun shooting from the 1980s till the early part of this century. It also led to a good number of competitors overloading the Super and blowing up guns.
Several things happened as a result. One was that the 9x23 Winchester developed (which was the same oal as the 38 Super) and the .356 TSW (which was a bit longer than the 9mm but could fit in guns made for the 9mm parabellum. The 38 Super Comp was also developed, a rimless 38 Super. These were 9mm cartridges in diameter. They got about 1400 fps with a 125 gr. bullet and were excellent cartridges.
But shortly after the appearance of these on the market the rules in IPSC changed. PF was lowered to 165. This meant that the standard 9mm could make major. This basically killed the market for these. Other changes were made as well.
So here...
https://www.americanrifleman.org/articles/2014/4/29/356-tsw/
http://www.ammo-one.com/356TWS.html
From
Forgotten Weapons:
https://www.youtube.com/watch?v=P2jU5cp4WCg
tipoc