If it is marked 2 1/2 and has not been modified you are taking your life in your hands putting 2 3/4 or 3" in it, putting to your face and pulling the trigger. If it is not marked and you are not sure do not shoot it with anything until you take it to a competent gunsmith who can check it for you. I have explained why below...
The reason is the old shells were "rolled crimped" and very little opened up as it unrolled to release the shot and card wad that held it in place. Todays shells are star crimped and extend much further into the forcing cone. This creates a restriction in the bore when fired in a gun with a short chamber. This restrictions spike the pressures inside the gun well above acceptable limits. The fact you have done it in the past does not make the practice any safer and puts undo strain on the gun. Eventually, when all the conditions are right, it IS gonna come apart and you DO NOT want to be on the receiving end of that, lifes to short.
The chambers can be lengthened to 2 3/4 (no steel, no magnum loads) and this would make it safe to shoot providing the rest of the gun in in good shape. I doubt anyone would suggest going to 3" with it. I don't doubt what you are saying but I am really suprised it functioned with three inch rounds and it really attests to the quality of these old guns in that it didn't come apart on you with the 3 inchers.. You can probably find a smith in the area that can do this very reasonably (under $100).
Now for your question IF you should do it. Depends on a couple of factors. If the gun is 95% or better I would say don't unless you do not care about the collector value. If it is just a well used shooter then the effect on its value as a collector is minimal.
If you want to shoot magnum 2 3/4 rounds &/or steel or 3" thumpers then you would be better suited (and safer) pickin up a used pump of recent manufacture that is designed to handle these loads safely.
This is just one ole shooters take on it, I am sure you will get others...
Dont
