History
The burning characteristics of black powder used in early cartridges meant that these cartridges operated at low pressures, generally under 25,000 psi (~172,369 kPa). These cartridges were limited by their case capacity, and the only way to get more power was to increase the case to hold more powder; this can be seen in firearms such as those made by Sharps Rifle Manufacturing Company, which made rifles with nominal powder capacities from 70 grains (.45-70) to 110 grains (.45-110).
With the advent of smokeless powder, which has a far greater energy density than black powder, it was possible to generate far more power in the large cases of the older black powder cartridges. Cartridges such as the .32-20 Winchester and .44-40 Winchester were chambered in both revolvers and lever action rifles, and the rifles' actions could handle much higher pressures. This led to "machine gun only" loads in these calibers, which provided far more velocity and energy in the rifles, but were not safe in the revolvers due to the higher pressures they generated. These loads were eventually dropped due to a combination of safety concerns, and new smokeless rifle cartridges that offered even higher velocities, such as the .30-30 Winchester.
The first modern smokeless powder cartridge deliberately loaded by a major manufacturer to higher than standard pressure was the .38 ACP, originally introduced in 1900. This cartridge provided performance similar to other .38 caliber cartridges of the time. However, in 1929 the cartridge was renamed the .38 Super Automatic, or just .38 Super, along with a significant increase in operating pressure and muzzle energy, making it the most powerful auto pistol cartridge available, in both energy and velocity, for many years. It was commonly found in the M1911 pistol, and was also available in the Thompson submachine gun. Like the "rifle only" loads, the .38 Super could still be chambered in the older .38 ACP guns, producing a dangerous combination. Capable of reaching a muzzle energy of 500 ft/lbs, the .38 Super remains a viable defensive cartridge, though it is most popular in shooting sports such as IPSC. A similar move to a high pressure loading was done on the .38 Special in 1930, producing the .38-44 HV loadings, and eventually leading to the development of the .357 Magnum.
Read more about this topic: Overpressure Ammunition
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