No wonder the neophyte is confused. In one place he finds Sherman Bell’s test results in the Winter 2001 DGJ article where he writes:
“With loads that are sensible in a light 2 1/2 inch gun, we see no dangerous pressure levels produced. I see no reason, related to safety, to modify an original 2 1/2 inch chambered gun to shoot 2 3/4 shells, if the 2 3/4 inch load you intend to use would develop pressure that is safe in that gun, when fired in a standard chamber.”
Then in another place he finds Larry Potterfield showing him how to lengthen the chamber of an antique Parker:
https://youtu.be/amBveFBnVgY