When I say hollow back I mean that the back is recessed not flat. IMO-not knowing much about casting- this would require a two piece mold probably of steel to withstand the heat. To make the mold I would guess it would take a lot of setup/programing and machine time which would have to be expensive. How else could it be done? Also-you indicated the poor quality had to do more with materials and processing not the mold. A simple lack of ideal materials during wartime could explain that-and as I said Tommy has found out some additional info which indicates a very good possible explanation as to what these are. I hope he will post it soon. If not -I will.
