The 1860's were converted to cartridges in 1871, Colt had to wait for the patent to expire that S&W had. It expired in 1869, and Colt started taking all of the 1860 percussion parts in inventory and made the cartridge conversions. Mine is actually an 1860 SA Army, but stamped 1871 when they would have converted it. Think that's how the story goes.
This is the one I have...so you are correct, I should refer to it by it's actual name...the 1860
https://www.cimarron-firearms.com/produ ... pe-ii.html
*Here we go, right from the website:
With his 1871 patent to convert percussion, front-loading revolvers to breech loading metallic cartridge arms, Colt employee Charles B. Richards was able to inexpensively convert the company's arms already in stock to the new self-contained cartridge system. Colt also produced a number of them, once the old percussion parts ran out, as newly manufactured breech loaders. This, the first truly practical method of updating their guns to handle the then-new metallic cased ammunition, allowed Colt to sell these sixguns at a competitive price of just a few dollars, compared to other metallic cartridge revolvers. In total, around 9,000 Richards Transition Models were manufactured between 1871-1878. Their low cost, combined with their modernization proved popular with folks, especially in the Western territories. Wild Bill Hickok was believed to have packed Richards conversions in his last years.