George, measure the chambers on that 16 you just picked up - it may very well be 3" chambered if it is anything like the two I currently own or the one I used to own. They ranged from a 1987 Upland Special to a 2012 Lightning Feather so I would not be surprised if yours fit in this too. I'm not saying this is a "good" thing but I could see it being of some advantage for using steel shot in one of these guns.
To the OP,
I've loaded 1 1/4 oz of shot into 16 ga hulls at various times. It can be a trick as it is a tight fit. My original load used Winchester 571 or Hodgdon HS-7 powder (same thing, different labels) using Remington SP-16 wads in Federal hulls. The powder used little space so the shot and wad was able to fit in with only light compression. After 571/HS-7 was discontinued, I tried a recipe using Blue Dot which is a bit bulkier. The amount of compression needed with the SP-16 wad was much greater and there were occasional crimps that would open in the box.
Today, Hodgdon Long Shot works as well as 571/HS-7 as LS is a pretty dense powder. One would still need to use a hull with a large internal volume such as Federal, Fiocchi, or Cheddite and it looks like the SP-16 would be the only one piece wad available, if one can find them.
