Monotype’s hot metal Bell series from 1931 was based on original types made by the punchcutter Richard Austin for the foundry of John Bell in the 1780s. The different sizes of Monotype’s series were not all based on the same model. As type historian James Mosley wrote on Typophile, “For 18 point and above (the metal type was cut in sizes up to 36 point) Monotype’s model was a larger type [than the model used for the text sizes], the ‘Great Primer’ cut by Austin. This has greater contrast in the capitals and a flat foot to letter a.” The digital Bell closely follows the design of the hot metal 18pt version, and is therefore somewhat lighter in color than the text sizes of Monotype’s original metal face.
James Mosley’s Typophile article can be found here.