Miller, your memory is good. 12 over C and the fractional gauge marks (12/1 etc) were both part of the rules of 1887.
"Choke" dates from 1875. All barrels with at least .008 constriction had to be marked choke, and the sender could request them to be marked choke with as little as .004 constriction. So no choke mark would mean cylinder or something very close.

Last edited by L. Brown; 05/19/17 09:08 AM.