1045 is too high in carbon for general case hardening. 1045 is a through hardening carbon steel. In the L C Smith Plans & Specifications book a matl spec chart is given. Both the frame & barrel specs show a 1020 steel. However under the Feather Weight drawings the drawing for the lug denoted a forging of 1020 steel but notes the barrel as approx 40 carbon, with actual grade not given.
This drawing is dated to Feb 19, 29. My guess is that at some point smith increased the carbon content of their barrel mat'l to give a "Harder" barrel.
Most case hardening was done on mat'l having no more carbon than around 20 points.
