JL - the idea is that a 20 gauge will go into the forcing cone and barrel of a 12 gauge gun. On the 2" chamber, it would have to if one was going to use longer hulls. The issue is whether there would be sufficient "meat" in the insert to deal with what might be near peak chamber pressure when the insert is chambered 2 3/4" and then adapted to a 2" 12 gauge chamber on the outside - obviously, the forcing cone reduction to bore diameter is 3/4" further back than when the 12 gauge chamber is 2 3/4". The front of the adapter is going to be pretty thin. Also, there might be higher pressure on the rapidly thinning barrrel walls of the 2" gun.
