The early 16 gauges were chambered for 2 9/16" shells and along with the 20 gauge (which were 2 1/2") were changed to 2 3/4" in 1925. I have seen 2 9/16 stamped on the barrels. And there have been people on this board who have said their 21s were stamped 2 9/16. Don't you remember us talking about it?