Quote from C. Sharps:
"The 1885 receiver frames and all internal parts are machined from solid steel, plate, bars and rod, in accordance with original dimensions and modern machining practices. Receiver frame is heat-treated 8620 steel and intended for use with rimmed cartridges."

It is my understanding the parts will interchange with original Winchester, and they are machined from the appropriate (8620) steel. Again, the knock to me is the octagon top and flat sides.