A Stamping is a cold forging just so we understand each other
There are 2 main types of malleable iron, white heart & black heart , it is all about the carbon distribution
I did a quick search to find a simple understandable comparrison and came up with this one ( ignore the pearlite bit as they were a much latter developement )
https://www.mecholic.com/2018/10/types-of-malleable-cast-iron.html
Of importance & it should answer questions about why a forging would be used in place of a casting, note the times taken to heat treat malleable iron as comparred to the single heat & hammer used to make a forging
people seem to think I could cast a 100 frame lugs today, machine them tomorrow the braize the frames the day after
but as you can see it is a lot longer process than that,
even worse in wartime because most interuptions to the heat treatments mean that entire batch becomes very expensive scrap metal
Early on in the history when BSA was making models with almost no common parts then malleable iron becomes the least cost method.
however as production volumes increase forgings become a lot cheaper.
This was one of the reasons for the redesign of the new 1936 range, to bring in economies of scale .
