Blondie's revolver is a 1851 Navy Colt model converted to shoot cartridges and is basically the same design as the Walkers, Dragoon models, and the 1860 Army in that the barrel wedge can be removed and barrel is removed, then the cylinder slips off the base pin in just a few seconds and easily reassembled, just like in the GB&U. :-)
The GB&U made in 1966 and was the third of a series with the man with no name, first was "A Fistfull of Dollars" then "A Few Dollars More".
Navy Conversion's were popular after the conflict, either as newly produced guns by Colt and also By Colt using up a surplus of existing parts, as well as some conversion's that were done by gunsmith/blacksmith types from their own shops. lots of folks had their original cap & ball pistols converted by Colt as the price was cheaper than buying a new 1873 Peacemaker.