Sadly, it looks like this saga is coming to an end. I've just heard back from Jeff Crozer at S&W who had this to say:

Good day,
Smith & Wesson will not cover any firearms that fail when reloaded ammunition is used. The failure you describe was probably the fault of the ammo and not the firearm.
I don’t know how to resolve this issue, perhaps we could replace the revolver at cost? I will contact the warranty center to review and discuss our options.
FYI, Mario has been retired for 6 months.
Regards,
Jeff

Jeffrey A. Croze
International Sales Manager
Smith & Wesson Corp/Thompson Center Arms

So there you have it, if you use reloaded ammunition in a S&W product, you are on your own.
And their "lifetime" service policy is only good until you use live ammo.
The part I don't get is that in today's litigious society, why they wouldn't put those things in great big bright red letters everywhere.
Oh well, I guess I've learned a valuable but expensive lesson.