Ahem..
Getting back to the model 646 revo in .40 cal for a minute: S&W first made them up in the Perf. Center division with competition in mind, IDPA in particular I believe. They had at least one problem which made them less-than-spectacular sellers. Due to the variations in .40 brass, moon clips of differing thicknesses were needed for reliable operation. (And, you'd have to mark the clips somehow to tell them apart.) Both the IDPAers I know who had this model spent much time sorting brass, and dropping loaded moon clips into their guns ahead of time, to make sure the cylinder would turn freely. Just conjecture on my part, but the 646s we see now are likely overruns from those early ones. Sales musta been less than brisk. Also guessing, but the cylinder being titanium would preclude most friendly local 'smiths from boring out the chambers to 10mm. Now don't let what I've stated above be seen as a condemnation of the 646. There's one in a shop near me that's been languishing in the display case for a couple months, priced at $519 or so. Wonder how he'd respond to an offer of $475?...Think he'd throw in extra clips, too?