At the risk of bringing accused of blasphemy on a double gun forum, his best answer might be a gas operated 28 gauge automatic.
That's what I did. My shoulder was extensively repaired, not replaced. Doc says if I injure it again, I get a titanium joint. Lots of physical therapy, and I was shooting doves 10 months after the surgery with a new Beretta A400 Upland, 3" chamber. Also shot ducks successfully with it, using 3" Hevi-XII factory shells. Gun turned out to be a lemon, would not cycle reliably, mostly a single shot. Gunsmith could not make it work, so I got a full refund. Having said that, I have a friend who has been shooting ducks with an A400 2-3/4" chamber gun for a few years, using the same 3" Hevi-XII with no issues. After dumping that Beretta, I went back to my Win SX3 20 ga with light loads, and got along fine. As my confidence and comfort improved, I stepped back to my Win SX3 12ga with light loads for ducks. The Beretta 28 was a nice gun, killed ducks just fine with the right ammo, did fine on doves with steel shot. Would have kept it if it had run properly. Hoping to go back to my O/Us, SxSs, and hammer guns this fall. Doc told me that I could shoot whatever does not hurt. If it hurts, don't do it.
