By moving the plug out to increase the weight of the projectile,it also increases the skirt thickness as the plug has a taper on it.

I used my Greener GP,24 inch barrel with a screw on paradox choke .
Also tried them in my Suhl & sohn SxS with smooth bores,24 inch barrels.
Hard to tell the accuracy in the double as no sights have been fitted as yet,however a 6-8 inch group at about 50 yards was achieved using both barrels.
Al