In my search for a Model 21 I ran into one for sale that had a slight bulge in the side of both barrels about 12 inches forward of the breech.  Gun was perfect in every other way.  Bores look perfect.  A friend of mine who is a quite knowledgeable Shotgun Guy suggested that perhaps someone bent the barrels to change point of impact.  He said the factory some times used that method to make adjustments.  If you have any thoughts about this please share.  Any ideas or info would be appreciated.  George