It looks like a brass framed copy of an 1851 Colt. Probably also in .44 caliber, rather than the .36 caliber that it should be, since it has a rebated cylinder and frame. ( The "step" in both parts. )
The short-barreled ones like that are usually marketed as a "Sheriff's Model".
Can't tell you much more than that from just the pic.
Any markings on it that you can make out? Possible manufacturer's name?
J.C.