Does the bolt lug fit solid in the frame slot?Hi Jake, unfortunately I do not know anyone else with an 1851, be nice if I did though. And there seems to be total of about 0.07 inches of 'slop' in the rotation of the cylinder with the hammer at full cock. This measurement is the same for all six positions. Additionally, the ratchet notches on the back of the cylinder seem to be unworn. It is hard to say about the state of the hand itself but the fact that it extends enough to engage the bolt and lock the cylinder leads me to believe that it is okay.
If markings on cylinder match frame indicating correct cylinder I wonder if the bolt has been replaced with too narrow of lug width or has been badly fitted.