Doc,
They got there size in Scotland where they originated (right ?)
What were they crossed with to make them bigger is what I do not know. Have you or your grandfather ever gotten a "red" from your black? I know it is a recessive gene that causes the red,once red always red.They tried to cull a the red early on and make black the only color,but a few red were saved to make a herd after World War II and imported to Canada. (At least that is what I understood)
I guess I am partial to the Angus because that is what my father and grandfather had were Black Angus(no papers on them though) I raised a few Reds for a few years,I do not have any cattle.. Are yours all the traditonal size?