Keith, Have a look at a clay gun owned by a "slammer" and you will see damage to the face of both barrel and breech that resembles pitting.Seen Browning's,Beretta's Perrazi's all the same This is wear. Thus the bolt dose not lock down proporly so the gun "springs" on each firing,thus increasing wear rate. If the gun then has the bite increased by what ever method you like with out ensuring the correct clearances on the wings etc[some new guns dont have this either] you create more trouble.

Dont want to labour the point Folks , but I do this for a living, 40 hours a week. I dont write books, I rebuild and repair double guns and have done for over 40 years so I think I speak with some knowlage of the subject.