Preparatory to my possible efforts to obtain a pair of Open Tops again, only in .44 Caliber this time, I was re-reading Mc Dowell's book on Colt Conversions and saw that there is at least one existing early 1872 Open Top in .44 Russian (Serial No. 6). I have heard of others having been found in .44 Russian (and 44-40 if you can believe it!) also. Considering the rim of the .44 Henry is actually larger, and the .44 Russian case is only .015" larger, it would be an easy to bore the cylinder and move the firing pin over.
Since my 1860 Henry rifle is .44-40, I have struggled with having an 1871/2 Open Top not in the same caliber as the rifle. The .44 Special is out, as it is post 1900. .44 Colt is a possibility, but from a historical sense, its .451" diameter bullet would be too large for the open top's bore of .432/.442". The soft .430" bullet of the .44 Russian would probably obdurate enough to be stable at pistol ranges.
As sexy as the .44 Colt is, I think the .44 Russian with its 246 grain bullet would be realistic, especially since there is/are original Open Tops in that caliber.... Besides, I already have 100 rounds of .44 Russian, 246 grain over Triple 7 loaded.