From the beginning, Smith 12g guns had 2 3/4" chambers, unless otherwise marked on the barrel flats.
Hunter Arms Company lengthened the 20 gauge chambers from 2 1/2" to 2 3/4" in 1936.
L.C. Smith and Hunter Arms Fulton 16 gauge guns manufactured as late as 1939 have been found with 2 9/16" chambers.