Tried to find a digitized 1931 edition of Burrard and could not.
Possibly greener4me could post an image of the relevant study he mentioned.

IMHO the point of knowing vintage shotshell pressures is that 1) there has been a great deal of misinformation and 2) we can know, not guess, the ballistics of the shells for which our vintage doubles were designed. OTOH it's perfectly fine to just shoot and be happy smile