What you'll find with the Elsie 16's factory chambered at 2 3/4" is that they're heavier in general than the earlier short-chambered 16's. (Hunter was the last of the American makers to switch to 2 3/4" standard chamber length in the 16ga.) I would not worry about modern 16ga ammo in an Elsie 16 with factory 2 3/4" chambers . . . except maybe the Federal 1 1/4 oz "magnums". Those might not hurt the gun, but they can be nasty on the shooter's shoulder.