1. There is
no justification for lengthening 2 5/8" chambers to 2 3/4"
2. There
might be some advantage in lengthening vintage 1/2" - 5/8" forcing cones...BY AN EXPERT. Done wrong = ruined barrel
Scroll down about 1/3 here for a summary of Sherman Bell's study which suggested than pressure might be decreased somewhat with a longer cone.
https://docs.google.com/document/d/1...vwLYc-kGA/edit
Because the angle of the cone is greater than the external taper of the barrels, in thick walled U.S. maker's 12g (but possibly not light British 12g game guns or small bores) there is usually greater wall thickness in the cone than at the end of the chamber (breech to right)
I still wouldn't do it
