??? Most "old west" style guns were/are Single Action (SA). (Yes there were a few DA that didn't go over well--mostly due to design/execution flaws "back then").
Also to the other poster's question--critical, again are you wanting an old Colt-style gun or one with aged or antiqued finish? There are a gazillion models/manufacturers of the former--among them, in no particular order:
-- Colt itself with its time-honored SAA design, priciest. (No antiques made, just new look)
-- Uberti (sold through "itself," Cimarron and Taylor's)..also antiqued versions sold.
-- Beretta (actually made by Uberti, a subsidiary now of Beretta)
-- Pietta (sold through EMF)
-- US Firearms (USFA) - second priciest. Also antiqued versions sold....and of course
--Ruger Vaquero (to 2005 and New Vaquero (2005 to present). Different internal workings from the Colt-based designs, and very hardy pieces. No antiued models, just new-look.
...and several, as suggest above, of the "aged or antiqued" look, including Cimarron's (
www.cimarron-firearms.com ) Uberti-made "original finish" available on several of their models, including the Model P ('73) and earlier replicas of percussion and (modern-modified) cartridge conversion guns (51s, 72s etc).
You mention 1860--do you literally mean 1860? Otherwise, the most popular "old west" gun over the years is the Colt 1873 SAA design. Remington joined the fray with its 1875 and 1890 models, and Smith & Wesson with its break-open "Scofield" model. These were all preceded by 1847 Colt Walkers, 1851 "Navy" and 1860 "Army" Colts, 1858 Remington, 1872 "open top" Colt, etc, etc. BUT the '73, aka Model P, aka Single Action Army or SAA, aka, Peacemaker, etc, is far and away what you see most (and 99% of TV and movies have portrayed).
EDIT: all of the cartridge guns fire modern-day (post 1900 or so) "smokeless" powders OR old-timey blackpowder. Just 'cause some like to shoot the BP--especially in old west reenactments--doesn't mean that modern-era guns can't shoot smokeless and is what most do. If you see a modern-day Colt SAA-design/replica gun that's described as "BP frame," it simply means it has some design features that are characteristic of that pre 1900 era gun.