It is most likely .38 S&W Special. For understandable reasons, manufacturers were (are) reluctant to help advertise for rivals. Thus, Colt came out with the .38 Colt Special, which was exactly the same cartridge as, and interchangeable with, the .38 S&W Special, but with a flat tip bullet.
Try checking the depth of the chambers. The .38 S&W case length was only 0.767", and the Special is much longer.
Try fitting some .38 Special fired cases into your chambers. The .38 S&W is a shorter, fatter case, and also will not fit into a .38 S&W Special chamber.