Oh yeah. We had this discussion.

5906TSW Replacement Barrel or 4006tsw conversion?

Short version is you can interchange slides between 9mm and .40S&W TSW pistols with no problem because the 5906TSW is built on a 4006TSW frame. You can also put a 5906tsw barrel into a 4006tsw slide to do an easy caliber conversion from .40 to 9mm. I have done this with no problems for accuracy or reliability, but do so at your own risk, and keep in mind that a regular 5906 barrel won’t work. Only the TSW versions will interchange.