Looks like Colt Model 1860 in .44 calibre cap&ball.
The rebated cylinder & that smooth rounded barrel are the dead give aways.
In anticipation of the hostilities leading to the Civil War, Samuel Colt manufactured quite a huge number of these (and many other models)to army the federal Union Army. This was quite a very popular model because it was the very first Colt .44 that could be easily carried on your belt. Unlike the earlier & heavier Walker & Dragoon .44 calibre Colt revolvers. The one and only drawback was the 1860 Model was not as powerful as the earlier 44s. Not such a big issue when shooting men versus buffalo or other big game in the American West.