In the early 1870s, Colt introduced the 38 Long Colt for use in revolvers originally designed for cartridges. This is merely the 38 (Short) Colt with a longer case, a heavier charge of blackpowder, and usually a heavier bullet of conventional design with the lubrication in grooves located below the case mouth. The 38 in the name reflects outside diameter of the case mouth. These revolvers used a significantly smaller chamber mouth and bore, so the 36-caliber bullet would fit without obturation. As such, accuracy was far superior to the best the inside lubricated 38 Short-Colt cartridges could offer when used in the conversion revolvers. With power and accuracy rivaling the best the 1851 cap-and-ball revolvers could do, these cartridge-revolvers rapidly gained wide popularity. Creation of the 38 Long Colt was not the last time the 38 Colt case was lengthened to create a newer and usually higher-pressure cartridge. See the 38 Special and 357 Magnum discussions. As with any revolver round, best practice is to apply a roll-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 crimp the case mouth. Generally, attempting to do both operations in one step is a recipe for damaged and destroyed cases.