For what it's worth, the original .38 LC military load was 17.8 grains of Black Powder, a 150 grain lead bullet, having a 10 shot average velocity 723 ft/sec (@25') from a 6" barrel.

For most of its earlier service life, the .38 LC was loaded with black powder, but in 1900, it was switched to smokeless. Woodin, et al, give the standard smokeless charge as being 3 grains of Bullseye and a 148 grain lead bullet.

For use in any .38 Special revolver (but not the earlier Colt .38 LC revolvers), there should be very little concern about just using normal .38 Special reloading data. I load .38 Short Colt (even shorter cases than .38 LC) with essentially .38 Special load data (using lead bullets), without problems when used in .38 Special revolvers.