Its not good to just substitute lead for jacketed. As Gun 4 Fun points out "lead slides through the bore so much easier" and with equal powder charge will have higher velocity than a jacketed bullet of the same weight. In my observations a lead bullet will have an equal velocity to the maximum loaded jacked bullet with the "start" load (or 10% less powder). Velocity is a limiting factor with lead, pushed too fast and you will have serious leading problems in your barrel. Because of the leading issue you will see in most data lead bullet loads have lighter maximum charges than jacketed, esp. in magnum cartridges running over 1,000 fps.

When using jacketed data for lead bullets of equal weight I'd suggest you reduce the maximum jacketed load by 20% for a start level load and consider the start level jacked data (10% reduction) as maximum. Work up your load looking for leading. If its leading at the forcing cone end you have a sizing problem or too light a load with a hard bullet. If its leading at the muzzle end or its leading the whole bore then you are pushing the bullet too fast and need to back down on your charge.

If you are looking for data using HP38 in the .357 mag with lead bullets you can find it at the Cartridge Loads - Hodgdon Reloading Data Center - data.hodgdon.com These loads are lighter cowboy level and all under 1,000 fps.

The Speer manual has + loads for 158gr lead bullets in the .38 spl.