Researcher does a good job of spelling it out. By WWII, standard chamber length for the 16ga in the US was 2 3/4", but it took some makers longer than others to get there. L.C. Smith was also very late in jumping on the 2 3/4" 16ga bandwagon. On p. 157 of Brophy's book, he shows a chart from 1936 that includes chamber lengths. By then, 2 3/4" was the standard for both 12 and 20ga Elsies. The 16 was still 2 9/16".