G'Day Fella's

Threadfin, the Mauser M66 concept, was way ahead of its time and I believe is the basis for the current batch of Blaser R93 / R8 "Would Be's", like the Chapuis and the Merkel!
I won't go as far as to say the Blaser R's are a descendant of the Mauser 66 but it wouldn't surprise me if Mr Blaser, once owned a Mauser M66!!!

As to the barrels that you mention, for this rifle.
They are different enough in bore diameter, that they can be used on quite a varied variety of game. So who ever chose them originally, had some knowledge and plans it would appear!

Hope the history lesson etc, has been of some assistance.

HooRoo
From
Homer