Watched it again last night. I loved the converted 1860. While in 1865, it would have been a long cylinder conversion, probably in .44 Henry, instead of another caliber.
That's why I took a Pietta 1860 Army, faux ivory grips, and a Kirst Saber river Konverter. In fact, despite the other CAS pistols I have (Colt 1873, 1872 Uberti Open Top, and 1851 .38 Konversion) I find that I pair my Saber River with my 1875 Schofield (also with faux ivory grips). That and my HRA 1860 are my primary CAS battery.
Between Saber River and Crossfire Trail, Selleck uses three favorite guns: 1860 conversion, 1875 Schofield and 1860 Henry.