Introduced in 1908 for the corresponding model of the Colt Automatic Pistol, original 38 Automatic Colt Pistol (ACP) loads used pressures that were subsequently deemed excessive. Load pressures was soon reduced to about 25,000 psi, which was relatively mild for the era. Because of this, performance was not up to the standard set by similar 9mm cartridges and guns from other manufacturers. For example, because the gun was made using better steel, which Germany then had almost exclusive access to, the 9mm Luger was loaded to about 33,000 psi and would therefore significantly outperform the 38 Colt. To add insult to injury, the 38 Colt is a semi-rimmed design for reasons no one will ever understand — evidently, in that era, some cartridge designers, such as Browning, just could not let go of the useless affectation of a rim on a case when superior headspace control methods existed. Considering that the semi-rimmed designs Browning insisted on using in several of his pistol-cartridge designs could not provide headspace control and that this design discouraged smooth magazine loading, cartridge feeding from the magazine, and action cycling. The continued use of semi-rimmed cases makes less than zero sense. The only reason the 38 Colt had any success in the market was the generally superior Browning-designed pistols in which it was chambered. As with any pistol round headspacing on the case mouth, best practice is to apply a taper-crimp after seating the bullet. This helps to lock the bullet in place against chambering forces that might otherwise drive it into the case. I cannot too-strongly recommend getting a second seating-and-crimping die so you can have one adjusted to only seat the bullet and the second adjusted to only taper-crimp the case mouth. Generally, attempting to do both operations in one step is a recipe for damaged and destroyed cases.