I had a 20 gauge Repro with two sets of original barrels, 26" and 28". It shot very nicely and was fun to shoot.
I bought a set of 16 gauge Galazan barrels for it and had Galazan fit the barrels for me.
The 16's were not nearly as much fun to shoot. The recoil was a bit much compared to any of my 16 gauge original Parkers. I never measured the chambers to see if their length was what was stamped on the barrels and I never paid any attention to the shape or contour of the cones... but I wonder what else besides the cones would have had this effect on felt recoil.