The original .38 Colt had an exterior lubed heeled bullet, and the brass was shorter version of the .38 Spl. I believe Colt changed the bullet to internal lubed bullet (.357) in about 1901. The chambers in the "new" version will have a "step" in the chamber.
When I reload for my Colt New Army, I just shorten a .38 Spl case to the shorter .38 Colt length and load them with 148 gr HBWCs as noted.