The folks like Jim Supica have evidentally not seen such an animal, as there's no mention of it in his books.
Can't find a reference to a 10" barrel in any of my resources, and I have a pretty good 'library'.
Obviously, that gun needs a letter, and lots of close-up, high-quality photos.
Points to ask about:
1) The grips appear to have been used considerably. The wear
indicators on the blued surfaces don't, particularly on the
2) Since all barrel-stock was alleged to have started life as 8-3/4"
would S&W have hand-forged a 10" barrel?
3) The front sight looks a bit odd...I can't find a 'twin' on any of my
IF the gun would letter, it could be a 'five-figure' example for sure.
To date, the rarest (and most-valuable) R.M. is the one-off .22lr caliber 8-3/4" example.
Please follow up on this gun, and keep the rest of us posted!
After all, this is the stuff that collectors and websites live for.