I would put zero reliance on that as a reason. Many of these old rifles had extremely optimistic leaves on their express sights. I think it was a form of marketing in the day, "Hey look, this 10 bore has leaves out to 300 yards! It must be a 300 yard capable 10 bore rifle!!! Yippe!"

Like calling every rifle a "Magnum" not long ago.

All of my DRs have optimistic sets of leaves from the 10 bore, the .450 and another BPE.