dnovo

Regarding your comment
"although I would venture to say that for every 375 Flanged double, there are 15 chambered in the belted, rimless H&H (and in the same ratio from the birthplace of both rounds, Holland & Holland.) "

Where did you get these figures from ?
Especially the "and in the same ratio from the birthplace of both rounds, Holland & Holland.)"

If the 2nd hand market of Doubles is anything to go by, I am not so sure that that many DR's have been made in 375H&H (ie NOT Flanged).

And I am not counting modern DR's like Chauis, Merkel etc
in the numbers - keep it old and English !!!