There could be considerable difference, as Ithaca kept beefing up their smallbore Flues as time went on. In the 1912 through at least 1915 Ithaca catalogues they give their smallbore weights as --

16-ga 5 3/4 to 6 1/4
20-ga 5 1/4 to 5 3/4
28-ga 4 3/4 to 5 1/4

In the July 1919, Ithaca catalogue --

16-ga 5 lbs. 14 ozs. to 6 1/2
20-ga 5 1/2 to 6
28-ga 5 to 5 1/2

In the December 1, 1919, Ithaca catalogue --

16-ga 6 to 6 3/4
20-ga 5 3/4 to 6
28-ga 5 1/4 to 5 3/4

In the 1925 Ithaca catalogue --

16-ga 6 1/4 to 6 3/4
20-ga 6 to 6 1/2
28-ga 5 3/4 to 6 1/4