It is indeed the Model 1A (Flayderman's designation, not the factory's), the first variation. The frame would originally have been silver plated (silver "washed") and the barrels blued. There were over 60,000 made c. 1859 but serial numbers started over after 60000.
Value in that condition runs around $500 or so if the grips are original, uncracked or chipped, and the gun is fully functional. The entire series, with several variations, was made up to 1874, still in the black powder era; firing with modern ammunition is not recommended.
Jim