John Browning designed the Models 1900 and 1902 Colt pistols for the .38 Automatic (aka .38 ACP and .38 Colt Automatic), which originally pushed a 130-grain bullet to 1,040 fps. Beginning in 1929, after development of the notably stronger Model 1911 pistol, Colt introduced the .38 Super Automatic (aka .38 Super and .38 Super +P), which was externally identical to the older .38 Automatic cartridge but loaded to much greater pressures. Early ballistics pushed a 130-grain bullet to 1,280 fps.

In 1974 the industry adopted the “+P” designation for cartridges that have two pressure limits, which led to the “.38 Super +P” designation to help prevent it from being chambered in the older Colt 1900 and 1902 pistols, which is dangerous and not recommended. Current industry maximum average pressure limits are established at 33,000 CUP, with none of the accompanying loads exceeding that figure.

The firearms industry has created some confusion with the .38 Super, as barrel groove diameters have been produced at .355, .356 and .357 inch (depending on manufacturer and when it was produced). As a result, data is offered with Hornady bullets measuring .355-inch (9mm) and .357-inch (designed for the .38 Special and .357 Magnum cartridges). It is suggested to slug your barrel and select bullets accordingly, or try both diameters to see which offers the best performance in a given gun.

Bullets should be seated to the correct overall cartridge length, then as a separate step, a taper crimp applied. The crimp applied to most factory loads (measured with blade calipers at the case mouth) is around .375 inch.

Several powders duplicated or exceeded factory load performance with notable performance observed with Alliant Power Pistol, Accurate AAC-7 and Vihtavuori VV-N105.

In spite of much .38 Super data using small rifle primers being published, Winchester Small Pistol primers were used exclusively here, which gave proper ignition and handled the pressures without issue. If this data is shot with small rifle primers, pressures will increase and powder charges must be reduced.