Originally Posted by DWalt

You are absolutely correct that the .38 S&W cartridge has a slightly larger diameter than the .38 S&W Special. .38 S&W chambers have a step in them at the case mouth position, and at that point the chamber diameter decreases enough to disallow the complete chambering of a .38 Special round. Therefore, the chamber must be bored more deeply to admit the longer .38 Special cartridge. Such modified chambers will then accept both cartridges. However, fired .38 Special cases will show a slight bulging due to their sloppy fit in the modified chamber. This is not considered unsafe, but some believe that split .38 Special cases may result. I have not found that to be the case.