 FACT: When Robin begins training the outlaws, we see an arrowhead  being cast, outdoors in a small mould. Next, we see an iron/steel  arrowhead being shaped on a stone. Iron or steel could not be cast,  outdoors and in the small quantity as shown, due to the heat needed.  The metal shown can only be pewter, lead or tin. To produce  arrowheads in those conditions, a friendly blacksmith would beat out  a suitably thin piece of waste metal, chop pieces off, then, others  could file or rub them to shape and sharpness.