Perhaps this topic could become a stickie? I have been using 38 Special data in 357 Magnum brass since about a year after I got my 357 Magnum in '87. I use data straight out of my manuals for loading 38 data in 357 brass, and no "formula". Just remember the listed data for 38 Special, velocities/pressure, in 357 brass will be higher than what is actually achieved. But on that same note; I have never had a bullet stuckm in my 4" 357's barrel, even wadcutters with 3.0 gr of Bullseye...