Altering the forcing cones longer usually reduces recoil slightly and improves pattern density.
This is something I did on a lot of shotguns and the owners seemed happy.
The forcing cone reamer I had would only cut the forcing cone, not the chamber length... so I simply ran it in as far as it would go. I usually used my lathe with the reamer powered, the feed controlled by the tail stock, and the barrels held by hand to keep them from rotating. About 60 rpm. By hand takes considerably longer.