It's a 'Thunder' in .41 Long colt. It's not a Peacemaker or a SAA; it is Colt's first commercial double action revolver. They made bunches of this model, though I think it was surpassed in popularity by its little brother the 'Lightning' in .38 Long Colt, which was patented in 1877.
Its trigger is a true DA, but it does not share with all modern DA revolvers the swing-out cylinder for reloading; it still has a little loading gate through which brass is ejected and cartridges are inserted one at a time. The spring work on these is tricky and delicate and hard to get repaired these days. Almost no-one makes ammunition for it anymore. Do NOT make the mistake of thinking that .41 magnum ammunition will work in this gun. If you could jam it in and get it to shoot, I'd guess it would blow a Thunder into shrapnel.