I can only provide what my Lyman Cast Bullet Handbook, 4th Edition says.
Under the .38 Special handgun data sheet, the Lyman #356242 (120 gr. round nose) section lists for Bullseye 2.8 grains as the starting load at 690 fps and 8,600 CUP.
Max load is 4.6 grains Bullseye at 1,001 fps and 16,400 CUP.
Test barrel was 4". Both loads were shown in bold, which Lyman uses to "designate potentially most accurate load" among all the powders and loads listed for each bullet section.