Coming to us from the now-defunct Triton
Cartridge Company, the .40 Super was, in result if not intent, a .400 Cor-Bon on steroids. Where the .400 used .45 ACP cases, the .40 used .451 Detonics cases cut to ACP length. To generate the performance desired, Triton also upped the operating pressure to 37,000 psi (well above the .45 ACP +P's pressure of 21,000 psi) and used Small Pistol primers in the cases.
This was too much for many shooters and some guns. I built a 1911 purposefully for .40 Super. It had a bank-vault lockup, a ramped, supported barrel and a heavy recoil spring. I quickly peened the rails where the barrel slammed down in unlinking. It took a lot of fussing over recoil springs, buffer pads and barrel fitting to get it to run and not beat itself to death. The .40 Super is not something you can manage with a simple drop-in barrel.
I solved the details just before I got around to having to install a compensator, and then I moved on to other cartridges.
Performance? Yowza! Out of a five-inch Government model, the .40 delivered 135-grain bullets at a smoking 1,800 fps, 165s at 1,500 fps and 200s at 1,300 fps. As I remarked when I first experimented with it, if you wanted to boost a 165-grain bullet faster than the .40 Super could, you needed something with a shoulder stock on it.
In an ironic shift from the .400 Cor-Bon, where speed was not enough, here it was too much. Muzzle blast was extreme, guns were hard to control and didn't last long. And when Triton folded, that was it. You can still get brass and loaded ammo, but you have to search.