Posed this question under the "Shotgun" forum and got two answers, one being, "ask a competent gunsmith."

So: Will a Fox Sterlingworth, 16 ga., Ser. #373XXX, mfg. by Savage after 1930, effectively handle HV (3 1/4 dram, 1 1/8 oz.) loads without damage? It's tight as a drum, as you'd expect, but thought I'd ask the experts.

I did note in an old '50s era "Gun Digest" that 3 1/2, 1 1/4 loads were available back then.

Thanks.

I have no personal experience with the Fox so this is just opinion but...
Make sure your chamber is 2-3/4 and not 2-5/8. A lot of pre-war 16's had the shorter chamber. If it is a 2-3/4 then you should have no problem with the 1-1/8 or even the 1-1/4 loads. The pressures are the same. But you may want to take a hard look at the stock. If your Fox is a nice light gun, a heavy diet of 1-1/4 oz loads may end up splitting the stock. Also you may want to pattern the gun with your intended loads. Often the lighter loads will throw better (denser) patterns, one of those rare occasions when less=more.
Hope this helps.
C.G.B.

I agree with CGB.