Yup. 38 Special brass is smaller diameter than 38 S&W. When you fire them, the brass fills the chamber and looks bulged. No problem there, but I am told by some that accuracy may suffer when not using the right brass.
38 S&W neck - .386"
38 Special - .379"
Correct bullets for a 38 S&W are .359", and .357" for 38 Special.