What Marrakai said! The fact is, the measurement you are asking for will only give you a starting point for regulating a double rifle with the same weight, barrel conture, and ballance, of the one measured. It still will not regulate the other rifle even when useing the same exact load!
Regulation is not an exact science, but starts with an educated guess,( the measurements you asked for) and must be completed by trial, & error, the way it has been done for 250 yrs. There are known reasons for this being the case, and I suggest you do a search on regulating a double rifle, on this forum, to get those reasons. They have been posted here many times!
It's old news to most of us, but if you can't find the strings pertaining to this subject, there are those here who can explain it again. Marakai is one who knows. I can explain it, but I don' t have the gift of makeing the most of the written word, like most here!