tipiguy: the 38 S&W is not the same case or bullet diameter as the 38 S&W Special. The 38 special takes a longer straight-walled case with a bullet diameter of .357-.358.
The 38 S&W takes a shorter, slghtly tapered case and uses a bullet of up to .360 diameter. That ebing said, current load ing data for that cartridge and a 158 gn bullet ranges from 1.8 gn of Bullseye for 607'/sec to 2.5 gn of Bullseye for 763'/sec. However, the British used that case as a basis for their 38-200 cartridge, which fired a 200 gn bullet at only 600 something ft/sec - and that cartridge was reputed to have been the field equivalent of the older 455 Webley round, which was a hair shorter on the power end than the 45 auto. Colonel Charles Askins used the 38-200 and spoke highly of it, so much so that after WWII his two favorite calibers were a 45 auto and the 38 Spl with the 200 gn load (slightly better than the 38 S&W).
I know that somewhere there is a currently available powder charge for the 38-200 that will work for ya. HTH. Mikey.