I bolded your comment above, but I think it was the firearm manufacturers' decisions to go with the 3" 20 gauge that was the demise of the 16 gauge.
My Dad had a Model 12 16 gauge 28" FC (1932 2-3/4") inherited from my grand father when he passed away. As was the custom in the 60's, he could not leave it alone and ordered a blond birdseye maple buttstock and fore-end from E.C. Bishop of Warsaw MO, and as he was a devoted follower/buyer of the Herter's (Waseca MN) catalog, and one Winter day in 1969 we stripped it down and reblued it with Herter's Belgian Blue (not a salt blue, per se) with a tank long enough for the barrel, mag tube and receiver. In the basement, we heated those parts in very hot water over two inline 2-burner Coleman stoves, swabbed the parts with the bluing solution, let it dry, and steel-wooled all of the "rust" before repeating the process 15 or more times. It turned out to be one of the best blue jobs I have seen since, and that includes the storied S&W blue.
Sorry to digress.
I am a dyed-in-the-wool Rem 870 12 gauge guy, but that Model 12 16 gauge was a pleasure to shoot and carry, being much lighter than my 26" 870. As it was lighter, the tendency to stop the gun was easy. I made my longest ever pheasant kill (a crossing shot) at 60 paces with it, and my Dad always insisted using #7-1/2 shot and I think a 2-3/4 dram load. I forget what the shot load was, but it smacked birds hard with that gun.
As a teenager in 69-70 I worked at Roberts Shooting Park in Elkhorn NE setting and pulling trap and skeet. There was a guy that shot a Win 12 16 gauge FC a lot from 16 yards and kept even with the 12 gauge guys or even out did them. He shot Rem Shur-Shot shells and allowed me to collect the empty hulls. They were low brass/high base shells and I talked my Dad into buying a set of Herter's 16 gauge reloading dies for his massive Herter's press for his ammo supply. Managed to order (from a local "sport" shop) 2 100 piece bags of 16 gauge one-piece wad columns for 1 oz. of lead shot due to the high base of the Rem hulls (12 gauge target loads at the time were 1-1/8 oz. using Win AA or Federal paper low-base hulls). We used Hercules Red-Dot back then and I think the charge was 17 grains. My Dad was ecstatic as 16 gauge shells back then were more spendy than 12 gauge shells.
Sorry to ramble. You guys bring up old memories and I reminisce. Shame on you! I can remember things from 50 years ago but have a hard time recalling what I had for dinner 3 nights ago.
Never get old.
Jim