Although your Fox 16 came with factory 2 3/4" chambers, at the time it was made, most 16ga shells were still 2 9/16". There were "heavy" 16's even in those short hulls: 1 1/8 oz shot. But that was over 3 drams equivalent of powder. The current 16ga "express" loads are 3 1/4 DE, 1 1/8 oz, which means more recoil than the more typical vintage loads. I would not worry about pressure since your gun is late 1930's and has factory 2 3/4" chambers, but recoil might be a concern. There used to be 2 3/4 DE, 1 1/8 oz 16ga loads. Significantly reduced recoil but still with a heavier shot charge. However, I don't think anyone is making those any more.
