The purpose of cast is to align the rear sight (eye) with the sighting line. Some need cast others don't, but the eye as any other rear sight, when moved a particular direction, makes the gun shoot that direction, to some amount. Take in to account the shooter's face, the taper of the stock and the angles before and after the bending. My impression is that for two barrels to impact so differently and it not be a regulation issue, the stock fit must be so poor that the gun is moving alot when mounted and assuming it is a twin trigger gun, the position of the hand factors as well. Onc e the gun is on the shoulder and to the face the alignment should be correct and both barrels should impact simularly, of course. For this not to happen, the barrels are not regulated or the position of the gun is changing. Bending the stock may help with the later.
