This is one of the 1200 '60 Colt Army cartridge conversions sent to the U.S government in 1871.  At the time S&W sent an equal number of .44 cal American models. These pistols were issued out to western cavalry units and subjected to very hard service. Colt eventually won the contract and the model 1873 S/A was issued to the troops. This pistol is one of the rarer ones that was nickel plated of which 20-30% remains.  It exhibits all the proper A and P inspector marks and has matching assemby numbers (876) throughout. The left barrel flat has the correct US and Ainsworth A. The grips fit well and have a minor repair at the forward toe.  The cylinder scene is about 90-95% visible and has a matching assembly number with the proper A and P under the Patent line.  All the mechanics functions well and the cylinder locks up tight. I 've owned 3 of these rare pistols in the past 35 years and this is the nicest one. A very hard pistol to acquire in any condition. 
Click on the (Enlarge) button when viewing the pictures. 

Sold