I've always had the understanding that basically during its early development stages, they were using 38 special cases but lengthened the cases 1/8" to prevent chambering the hot new round into revolvers designed for 38 special to keep the revolvers from blowing up from the additional pressure. The new revolver designed to accept the new cartridge was the "Registered Magnum" or model 27, which came out in 1935.


As far as loading 38 special or 357 magnum, which I reload both. Stick to published info found in reloading books and you'll be fine.