Your 30-1 is simply an evolutionary development of the design series that included your Regulation Police a few decades earlier. They stretched the frame slightly to accommodate a long enough cylinder for the 38 Spl and changed the mainspring from leaf type to a coil spring. The Model 31-1 was the actual replacement for the Regulation Police because they also added to the grip frame to make it square. The earlier I-frame came in 22 LR, 32 S&W Long and 38 S&W. The J-frame added the 38 Spl, then 32 H&R Mag, and eventually 357 Mag and 327 Fed Mag.
You've already heard from my "coconspirators" with the small frame guns, David and Jim, so you know we are very enthusiastic about S&W's most compact and elegant revolvers. Welcome to the madness!
Froggie