I'd note here that not all manufacturers changed to 2 3/4" chambers at the same time. And individual makers changed different gauges to the then-new 2 3/4" standard at different times. For example, virtually all pre-WWII Hunter Arms (LC Smith) 16's are 2 9/16". I think they were about the last American maker to make the switch--certainly later than Ithaca and Savage--even though they had gone to 2 3/4" in the 12 and 20 several years earlier.