The one thing I'm sure of is that your 2 3/4" 1100 will not function as a 3" no matter which barrel you put on it. That's why they make two different models. I own both and the only difference I see is that the 2 3/4" barrels have two gas ports and the 3" barrels only require one based on light and heavy load pressures. I'm not positive, but I think the recoil spring is the same in both models and everything is controled by the gas ports. I beleive the main difference in the receivers is where the extractor is located, but like most guys have said "your local gunsmith can elaborate on all of this if he's worth his salt".

Boldt