.38 Not So Super
For the time, .38 Super was pretty special. Okay, poor choice of words. It was powerful, at least moreso than most other handgun calibers of the early 1900s. In the first few decades of the 20th century, your choice of handguns was mostly limited to big, heavy, slow moving bullets like the .45 ACP, or small slow moving bullets like the original standard pressure .38 Special. The .38 Super was one of the first handgun cartridges that relied on velocity, rather than size, to get results.
A .45 ACP will work against vulnerable, squishy targets like the enemies of the US military, but it’s not known for its penetrating power. A 130 grain bullet from a .38 Super travels at over 1300 fps, and could penetrate the ballistic vests and car bodies of the 1930s. You might think a cartridge like that would have been a dream come true for law enforcement stuck in the arms race of the violent depression/prohibition-era gang violence. And it might have been, had the .38 Super not been completely overshadowed by the arrival of .357 magnum in 1934.
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Forget the fact that a 1911 in .38 Super holds four more rounds than a six shooter (9-round mags, plus the chamber). And who cares if it has less recoil and is easier to reload? The .357 was supposed to be a man-stopper of mythological proportions. Like the .38 Super, the .357 magnum could lob a bullet at 1300 fps. Only it could do that with 180 grains instead of just 130. The magnum was a huge ballistic leap forward, and much more attractive to an American law enforcement culture that would not be ready to embrace automatic pistols for another half century.
So cops kept their wheel guns for another few decades, some switching to the new .357 magnum, but most sticking with their .38 specials. WWII hit, and Colt shifted into full-time war production. It seemed like there was no place for the .38 Super, and the cartridge nearly slipped into extinction.