The S&W Model 2, though never officially adopted by the military, was nicknamed the "Army" or "Old Army" because of its popularity with the soldiers. Many officers liked to carry them because the copper cartridges were unaffected by moisture and could be left in the gun for long periods.

I have letters from a Wisconsin soldier who says (in early 1865 at Petersburg) that he carries "a revolver that would take a man at 40 rods. I can hit a 3 inch ring 10 rods every time…it carys copper cartridges and can be loaded in 15 seconds." Most probably it was a Model 2.

I'm not a firearms expert and there is some disagreement when the Model 2 was first produced -- some say 1861 and others 1865, but IAC it was documented to have been used in the CW.

Here are a couple of web pages on it.

http://armchairgunshow.com/SWTU-info.html
http://www.model2project.com/
http://www.model2project.com/examples.html