It should have a makers mark on it somewhere. It may be hidden under the loading lever. It's most likely to be ASM or one of the lesser known ones like PR or COM. Usually a PR gun has a superposed PR on the butt next to FIE like this one.
If its a Pietta it may have FAP under the lever like this one. FAP may be in a diamond
ASP will have DGG arranged in a circle.
Uberti will have a U in an octagon. Its not likely to be a Uberti with a brass frame tho.
Palmetto will be a palm tree in a circle.
COM will be marked COM
ASM will be marked ASM or SM