The barrel is chambered for 2 3/4" shells. DON'T shoot 3" shells in it- it's not safe, as the mouth of the shell opens out into the forcing cone of the barrel and further constricts it, just at the time chamber pressure is at its highest. Not what you want to be doing...
Your receiver (ejector) is set up for 2 3/4" shells too.
You want to shoot 3" or 3.5" shells, get a gun set up to handle them. Leave the gun you have to the size shells it was built to handle. A Winchester 1300 will handle 3" shells, I don't know if Winchester ever built a shotgun for 3.5" shells.
fwiw,
lpl