Ah Ha, and Since You Asked
Don't really have a Clue. Or: Histeraclly (yes it's miss-spelled), the 1851 Navy became the most celebrated, natural pointing, bestest balanced, superist hand gun of the age. Then carried forward to the present time with the exact same accolade. Not that the 1851 isn't all of those things, it certainly is (according to legend). And, it has the ubiquitous Octagon Barrel.
Now, in plain fact, the 1861 is an 1851. Same frame, same clockworks, same cylinder, etc. The big departure is the 1860esque barrel assembly. Which is described by many as "sleek and sexy." I happen to like the 1861 even though I have a penchant for Octagonal Barrels. But, were one to consider the now defunct line of Armi San Marco Richards conversions, which were built primarily on the 1851 frame with the 1861 barrel assembly, which actually makes them 1861s, they are without doubt, the sleekest and sexiest SAs or Conversions ever. Even if they are/were a Hysterical No No.
Now, I go back to the 1861 being unappreciated. It is Unappreciated. I don't have a clue why. Perhaps if W. B. Hickok had preferences the 1861, it would be held in higher acclaim.
I know, were I to build a new personal set of 38 cartridge conversions, I'd start with Pietta 1861s. Chop Chop Shaka Laka.
Lets Have Fun Out There