Not a fine gun question, but you guys seem to know everything.
This is what I think I know:
Benelli is still .726 even with the new Ciro
Browning invector plus .733?
Beretta ciro plus .726???
Mossberg 835 & 935 .750
Perazzi .736
Please add or correct thanks.

With all these variations in bore diameter of the 12ga I am forced to admit that perhaps it would better be called a 12 bore then a 12gauge as it seems a standardization of bore diameter no longer exists.
What a revolting development!