.38 ctg? .38 s&w ctg?
If you're asking about the .38 S&W, it's not interchangeable with .38 Special. .38 special is too long to fit in a .38 S&W gun. .38 S&W case is too fat to fit in a .38 Special gun. The projectile is also fatter than .357.
Editing: Oh, yeah, if you could fit a .38 special round in a .38S&W gun, don't pull the trigger. The .38 Special round is too powerful for the .38 S&W gun.
Regards.