JR' The point I wanted to point out was that The word 'Gauge' headed up the left-hand column, and the word Bore is used for the Choke constriction.Just an Observation from a Old London Gunmaker! As to the Definition of Receiver/Action, I willnot comment....McIntosh and I went Round & Round,and Round yet again, when we were writing Vol.1 of Shotgun Tech. But what about this 'Water-Table'?...My Old 'Matey" from the Ejector-Shop at JP&S(1953-1970)felt it came from the British Navy where they had a 'Plimsole' Line around the Ship?????? DT/cc