Notice how I keep the loading lever out of the way. I drilled, tapped, and used a screw as a stop, so the plunger won't go past a certain spot. I thought it was better than string or tape...The old gun ain't real purdy, but it's a good shooter.
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.