1. Colt 1860 Army .44 made 1862
2. Colt 1851 Navy cartridge conversion, Richards-Mason design.
A low number like that is probably one of the ones assembled out of parts on hand in the 1870s and numbered in its own series 1-3800. I guess it might be a very early gun returned for conversion by an individual.
Does it have any patent dates or other legible markings on it?